소스중에
<? if ($is_guest) { ?>
로 시작되는 부분을

<? if ($is_guest) { ?>
<tr>
    <td class=write_head><img id='kcaptcha_image' /></td>
    <td><input class='ed' type=input size=10 name=wr_key itemname="자동등록방지" required>&nbsp;&nbsp;왼쪽의 글자를 입력하세요.</td>
</tr>
<tr><td colspan=2 height=1 bgcolor=#e7e7e7></td></tr>
<? } ?>
--> 얘로 바꾸시구요.
아래 자바스크립트 부분에

document.getElementById('btn_submit').disabled = true;
--> 얘 윗쪽에

    if (!check_kcaptcha(f.wr_key)) {
        return false;
    }
얘를 삽입하세요...

if (typeof(f.wr_key) != 'undefined') {
        if (hex_md5(f.wr_key.value) != md5_norobot_key) {
            alert('자동등록방지용 글자가 제대로 입력되지 않았습니다.');
            f.wr_key.select();
            f.wr_key.focus();
            return false;
        }
    }

얘를 삭제하시고
    if (!check_kcaptcha(f.wr_key)) {
        return false;
    }
얘를 넣으세요...

은동이님 소스 그대로 퍼다가 테스트 해보니 (전 그누 최신버전) 오히려 다른 에러가 나네요.
아래 소스 복사해 붙여 보세요.
아마 불필요한 소스들을 삭제하시면서 뒤섞인 것 같아요.
<?
if (!defined("_GNUBOARD_")) exit; // 개별 페이지 접근 불가

if ($is_dhtml_editor) {
    include_once("$g4[path]/lib/cheditor4.lib.php");
    echo "<script src='$g4[cheditor4_path]/cheditor.js'></script>";
    echo cheditor1('wr_content', '100%', '250');
}
/*
성명 name
성별 wr_1
주민등록번호 wr_2
양력음력 wr_3
생년월일 년 월 일 wr_4
연락처 전화, hp wr_6, 7
우편번호 wr_5
주소 wr_subject
직업 wr_8
이메일 wr_email
홈페이지 wr_homepage
납부방법 wr_9
후원금액 wr_10
*/

//주민등록번호
$min = explode("-",$write[wr_2]);
$min1  = $min[0];
$min2  = $min[1];

//생년월일
$birth = explode("-",$write[wr_4]);
$birth1  = $birth[0];
$birth2  = $birth[1];
$birth3  = $birth[2];

//우편번호
$ext5 = explode("-",$write[wr_5]);
$ext5_00  = $ext5[0];
$ext5_01  = $ext5[1];

//전화번호
$tel = explode("-",$write[wr_6]);
$tel1  = $tel[0];
$tel2  = $tel[1];
$tel3  = $tel[2];

//휴대전화
$hp = explode("-",$write[wr_7]);
$hp1  = $hp[0];
$hp2  = $hp[1];
$hp3  = $hp[2];

?>

<script type="text/javascript">
function onlyNumber(obj) {
if(isNaN(obj.value)){
alert('숫자만 입력해 주세요');
obj.value=obj.value.substr(0,obj.value.length-1)
}
}
</script>

<div style="height:14px; line-height:1px; font-size:1px;">&nbsp;</div>

<style type="text/css">
.hu_tb{width:98%; border:2px solid #999; border-collapse:collapse;}
.hu_tb td{border:1px solid #cdcdcd; padding:5px;}
.write_head { width:100px; height:30px; padding-right:15px; text-align:right; color:#363636; background-color:#efefef;}
.field { }
.ed{border:1px solid #ddd; height:18px;}
</style>

<script language="javascript">
// 글자수 제한
var char_min = parseInt(<?=$write_min?>); // 최소
var char_max = parseInt(<?=$write_max?>); // 최대
</script>

<form name="fwrite" method="post" onsubmit="return fwrite_submit(this);" enctype="multipart/form-data" style="margin:0px;">
<input type=hidden name=null>
<input type=hidden name=w        value="<?=$w?>">
<input type=hidden name=bo_table value="<?=$bo_table?>">
<input type=hidden name=wr_id    value="<?=$wr_id?>">
<input type=hidden name=sca      value="<?=$sca?>">
<input type=hidden name=sfl      value="<?=$sfl?>">
<input type=hidden name=stx      value="<?=$stx?>">
<input type=hidden name=spt      value="<?=$spt?>">
<input type=hidden name=sst      value="<?=$sst?>">
<input type=hidden name=sod      value="<?=$sod?>">
<input type=hidden name=page    value="<?=$page?>">

<table width="<?=$width?>" align=center cellpadding=0 cellspacing=0><tr><td>

<h3 class="font_nanum" style="color:#336699;">
대리점신청하기
<? if ($member['mb_level'] >= 7) { ?>
| <a href="./board.php?bo_table=<?=$bo_table?>">신청현황보기</a>
<? } ?>
</h3>

<table class="hu_tb">

<?
$option = "";
$option_hidden = "";
if ($is_notice || $is_html || $is_secret || $is_mail) {
    $option = "";
    if ($is_notice) {
        $option .= "<input type=checkbox name=notice value='1' $notice_checked>공지&nbsp;";
    }
/*
    if ($is_html) {
        if ($is_dhtml_editor) {
            $option_hidden .= "<input type=hidden value='html1' name='html'>";
        } else {
            $option .= "<input onclick='html_auto_br(this);' type=checkbox value='$html_value' name='html' $html_checked><span class=w_title>html</span>&nbsp;";
        }
    }
*/
    if ($is_secret) {
        if ($is_admin || $is_secret==1) {
            $option .= "<input type=checkbox value='secret' name='secret' $secret_checked><span class=w_title>비밀글</span>&nbsp;";
        } else {
            $option_hidden .= "<input type=hidden value='secret' name='secret'>";
        }
    }
   
    if ($is_mail) {
        $option .= "<input type=checkbox value='mail' name='mail' $recv_email_checked>답변메일받기&nbsp;";
    }
}

echo $option_hidden;
if ($option) {
?>
<tr>
    <td class=write_head>옵 션</td>
    <td><?=$option?></td></tr>
<tr><td colspan=2 height=1 bgcolor=#e7e7e7></td></tr>
<? } ?>

<tr>
    <td class=write_head>이 름*</td>
    <td><input class='ed' maxlength=20 size=15 name=wr_name itemname="이름" required value="<?=$name?>"></td>
</tr>

<tr>
    <td class=write_head>성별</td>
    <td>
<input type="radio" name=wr_1 itemname="성별" value="남" <?if($write[wr_1] == "남") echo "checked"?>>
남
<input type="radio" name=wr_1 itemname="성별" value="여" <?if($write[wr_1] == "여") echo "checked"?>>
여 </td>
</tr>

<tr>
    <td rowspan="2" class=write_head>생년월일</td>
    <td>
<input name='birth1' class=ed value='<?=$birth1?>' type='text' size='4' maxlength='4' onkeydown='onlyNumber(this);'  itemname='년'>년
<input name='birth2' class=ed value='<?=$birth2?>' type='text' size='2' maxlength='2' onkeydown='onlyNumber(this);'  itemname='월'>월
    <input name='birth3' class=ed value='<?=$birth3?>' type='text' size='2' maxlength='2' onkeydown='onlyNumber(this);'  itemname='일'>일
<!-- input class='ed' maxlength=20 size=15 name=wr_4 itemname="생년월일" required value="<?=$write[wr_4]?>"></td></tr -->
<input type="radio" name=wr_3 itemname="음양" value="양력" <?if($write[wr_3] == "양력") echo "checked"?>>양력
<input type="radio" name=wr_3 itemname="음양" value="음력" <?if($write[wr_3] == "음력") echo "checked"?>>음력 </td></tr>

<tr>
    <td>
<!-- input class='ed' name=wr_2 itemname="주민등록번호" required value="<?=$write[wr_2]?>" --></td>
</tr>

<tr>
    <td class=write_head>전화번호*</td>
    <td>
<!-- 전화번호 시작 -->
<select name='tel1' class='ed'  itemname='전화번호'>
<option value='010' <? if($tel1 == "010") echo "selected"; ?>>010</option>
<option value='011' <? if($tel1 == "011") echo "selected"; ?>>011</option>
<option value='016' <? if($tel1 == "016") echo "selected"; ?>>016</option>
<option value='017' <? if($tel1 == "017") echo "selected"; ?>>017</option>
<option value='018' <? if($tel1 == "018") echo "selected"; ?>>018</option>
<option value='019' <? if($tel1 == "019") echo "selected"; ?>>019</option>
        <option value='02' <? if($tel1 == "02") echo "selected"; ?>>02</option>
        <option value='031' <? if($tel1 == "031") echo "selected"; ?>>031</option>
        <option value='032' <? if($tel1 == "032") echo "selected"; ?>>032</option>
        <option value='033' <? if($tel1 == "033") echo "selected"; ?>>033</option>
        <option value='041' <? if($tel1 == "041") echo "selected"; ?>>041</option>
        <option value='042' <? if($tel1 == "042") echo "selected"; ?>>042</option>
        <option value='043' <? if($tel1 == "043") echo "selected"; ?>>043</option>
        <option value='051' <? if($tel1 == "051") echo "selected"; ?>>051</option>
        <option value='052' <? if($tel1 == "052") echo "selected"; ?>>052</option>
        <option value='053' <? if($tel1 == "053") echo "selected"; ?>>053</option>
        <option value='054' <? if($tel1 == "054") echo "selected"; ?>>054</option>
<option value='055' <? if($tel1 == "055") echo "selected"; ?>>055</option>
        <option value='061' <? if($tel1 == "061") echo "selected"; ?>>061</option>
        <option value='062' <? if($tel1 == "062") echo "selected"; ?>>062</option>
        <option value='063' <? if($tel1 == "063") echo "selected"; ?>>063</option>
        <option value='064' <? if($tel1 == "064") echo "selected"; ?>>064</option>
<option value='070' <? if($tel1 == "070") echo "selected"; ?>>070</option>
        <!-- <option value='064' <? if($tel1 == "064") echo "selected"; ?>>0505</option>
        <option value='064' <? if($tel1 == "064") echo "selected"; ?>>0303</option> -->
<!-- <option value='0505' <? if($tel1 == "0505") echo "selected"; ?>>0505</option> -->
      </select> -
      <input name='tel2' class=ed value='<?=$tel2?>' type='text' size='4' maxlength='4' required onkeydown='onlyNumber(this);'  itemname='전화번호 두번째자리'>  -
      <input name='tel3' class=ed value='<?=$tel3?>' type='text' size='4' maxlength='4' required onkeydown='onlyNumber(this);'  itemname='전화번호 세번째자리'>
<!-- 전화번호 끝 --> </td>
</tr>


<tr>
    <td class=write_head>휴대폰<br />
      (연락받을번호)*</td>
    <td>
<!-- 휴대폰 시작 -->
<select name='hp1' class='ed'  itemname='휴대전화' >
        <option value='010' <? if($hp1 == "010") echo "selected"; ?>>010</option>
        <option value='011' <? if($hp1 == "011") echo "selected"; ?>>011</option>
        <option value='016' <? if($hp1 == "016") echo "selected"; ?>>016</option>
        <option value='017' <? if($hp1 == "017") echo "selected"; ?>>017</option>
        <option value='018' <? if($hp1 == "018") echo "selected"; ?>>018</option>
        <option value='019' <? if($hp1 == "019") echo "selected"; ?>>019</option>
      </select> -
      <input name='hp2' class=ed value='<?=$hp2?>' type='text' size='4' maxlength='4' required onkeydown='onlyNumber(this);'  itemname='휴대전화 두번째자리'>  -
      <input name='hp3' class=ed value='<?=$hp3?>' type='text' size='4' maxlength='4' required onkeydown='onlyNumber(this);'  itemname='휴대전화 세번째자리'>
  <!-- 휴대폰 끝 --> </td></tr>
<tr>
    <td class=write_head>우편번호</td>
    <td>
<input class=ed size="4" name=ext5_00 itemname="우편번호 앞자리"  readonly value="<?=$ext5_00?>"> -
<input class=ed size="4" name=ext5_01 itemname="우편번호 뒷자리"  readonly value="<?=$ext5_01?>">
&nbsp;<a href="javascript:;" onclick="win_zip('fwrite', 'ext5_00', 'ext5_01', 'wr_subject', 'wr_subject');"><img src="<?=$board_skin_path?>/img/addrsearch.gif" border=0 align="absmiddle"></a> </td></tr>


<tr>
    <td class=write_head>상세주소</td>
    <td>
<input class="ed" style="width:60%;" name=wr_subject id="wr_subject" itemname="상세주소"  value="<?=$write[wr_subject]?>"> </td></tr>

<tr>
    <td class=write_head>업체명</td>
    <td>
<input class='ed' name=wr_8 itemname="직업" value="<?=$write[wr_8]?>"></td></tr>

<? if ($is_email) { ?>
<tr>
    <td class=write_head>이메일</td>
    <td><input class='ed' maxlength=100 size=43 name=wr_email email itemname="이메일" value="<?=$email?>"></td></tr>
<? } else {  ?>
<tr>
    <td class=write_head>이메일</td>
    <td><input class='ed' maxlength=100 size=43 name=wr_email email itemname="이메일" value="<?=$member[mb_email]?>"></td></tr>

<? } ?>

<? if ($is_homepage) { ?>
<tr>
    <td class=write_head>홈페이지</td>
    <td><input class='ed' size=43 name=wr_homepage itemname="홈페이지" value="<?=$homepage?>"></td></tr>

<? } ?>

<tr>
    <td class=write_head>PDR WEBASTO에게 전하실 말씀*</td>
    <td>
            <? if ($is_dhtml_editor) { ?>
            <?=cheditor2('wr_content', $content);?>
            <? } else { ?>

            <textarea id="wr_content" name="wr_content" class=tx style='width:90%; word-break:break-all; border:1px solid #ccc;' rows=5 itemname="내용" required
        <? if ($write_min || $write_max) { ?>onkeyup="check_byte('wr_content', 'char_count');"<?}?>><?=$content?>
            </textarea>
            <? if ($write_min || $write_max) { ?>
            <script language="javascript"> check_byte('wr_content', 'char_count'); </script>
            <?}?>
            <? } ?>    </td>
</tr>



<? if ($is_guest) { ?>
<tr>
    <td class=write_head><img id='kcaptcha_image' border='0' width=100 height=40 onclick="imageClick();" style="cursor:pointer;" title="글자가 잘안보이는 경우 클릭하시면 새로운 글자가 나옵니다."></td>
    <td><input class='ed' type=input size=10 name=wr_key itemname="자동등록방지" required>&nbsp;&nbsp;<span style="color:#ff0000;">자동로봇 등록방지 - 왼쪽의 글자를 입력하세요.</span></td>
</tr>

<? } ?>
</table>



<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
    <td width="100%" align="center" valign="top" style="padding-top:30px;">
        <input type=image id="btn_submit" src="<?=$board_skin_path?>/img/submit.jpg" border=0 accesskey='s'>&nbsp;
</td>
</tr>
</table>

</td></tr></table>
</form>
<div style="height:20px;"></div>

<script type="text/javascript" src="<?="$g4[path]/js/jquery.kcaptcha.js"?>"></script>
<script type="text/javascript">

<?
// 관리자라면 분류 선택에 '공지' 옵션을 추가함
if ($is_admin)
{
    echo "
    if (typeof(document.fwrite.ca_name) != 'undefined')
    {
        document.fwrite.ca_name.options.length += 1;
        document.fwrite.ca_name.options[document.fwrite.ca_name.options.length-1].value = '공지';
        document.fwrite.ca_name.options[document.fwrite.ca_name.options.length-1].text = '공지';
    }";
}
?>

with (document.fwrite)
{
    if (typeof(wr_name) != "undefined")
        wr_name.focus();
    else if (typeof(wr_subject) != "undefined")
        wr_subject.focus();
    else if (typeof(wr_content) != "undefined")
        wr_content.focus();

    if (typeof(ca_name) != "undefined")
        if (w.value == "u")
            ca_name.value = "<?=$write[ca_name]?>";
}

function html_auto_br(obj)
{
    if (obj.checked) {
        result = confirm("자동 줄바꿈을 하시겠습니까?\n\n자동 줄바꿈은 게시물 내용중 줄바뀐 곳을<br>태그로 변환하는 기능입니다.");
        if (result)
            obj.value = "html2";
        else
            obj.value = "html1";
    }
    else
        obj.value = "";
}

function fwrite_submit(f)
{
    /*
    var s = "";
    if (s = word_filter_check(f.wr_subject.value)) {
        alert("제목에 금지단어('"+s+"')가 포함되어있습니다");
        return false;
    }

    if (s = word_filter_check(f.wr_content.value)) {
        alert("내용에 금지단어('"+s+"')가 포함되어있습니다");
        return false;
    }
    */

    if (document.getElementById('char_count')) {
        if (char_min > 0 || char_max > 0) {
            var cnt = parseInt(document.getElementById('char_count').innerHTML);
            if (char_min > 0 && char_min > cnt) {
                alert("내용은 "+char_min+"글자 이상 쓰셔야 합니다.");
                return false;
            }
            else if (char_max > 0 && char_max < cnt) {
                alert("내용은 "+char_max+"글자 이하로 쓰셔야 합니다.");
                return false;
            }
        }
    }

    <?
    if ($is_dhtml_editor) echo cheditor3('wr_content');
    ?>


    var subject = "";
    var content = "";
    $.ajax({
        url: "<?=$board_skin_path?>/ajax.filter.php",
        type: "POST",
        data: {
            "subject": f.wr_subject.value,
            "content": f.wr_content.value
        },
        dataType: "json",
        async: false,
        cache: false,
        success: function(data, textStatus) {
            subject = data.subject;
            content = data.content;
        }
    });

    if (subject) {
        alert("제목에 금지단어('"+subject+"')가 포함되어있습니다");
        f.wr_subject.focus();
        return false;
    }

    if (content) {
        alert("내용에 금지단어('"+content+"')가 포함되어있습니다");
        if (typeof(ed_wr_content) != "undefined")
            ed_wr_content.returnFalse();
        else
            f.wr_content.focus();
        return false;
    }

    if (!check_kcaptcha(f.wr_key)) {
        return false;
    }


    document.getElementById('btn_submit').disabled = true;

<?// if ($member['mb_level'] >= 7) { ?>
  // document.getElementById('btn_list').disabled = true;
<? //} ?>

    <?
    if ($g4[https_url])
        echo "f.action = '$g4[https_url]/$g4[bbs]/write_update.php';";
    else
        echo "f.action = './write_update.php';";
    ?>
   
    return true;

}
</script>

<script language="JavaScript" src="<?="$g4[path]/js/board.js"?>"></script>
<script language="JavaScript"> window.onload=function() { drawFont(); } </script>

이대로 테스트 해 봤는데, 잘 됩니다.
계속해서 글쓰기에는 $wr_id 값을 사용하지 않습니다. 라는 오류가 나오면,
write_update.skin.php 파일을 봐야 할 것 같아요.