You should be sure to add in the .js includes... I thought you had done that already.
Code:
<script type="text/javascript" src="clientscript/vbulletin_profilefield_edit.js?v=$vboptions[simpleversion]"></script>
<!-- ########## WHATS ON YOUR MIND ######### -->
<tr><td class="alt1" nowrap align="left">
<fieldset>
<a href="/profile.php?do=editprofile"><img src="/image.php?u=$bbuserinfo[userid]" alt="Some avatar" border="0" /></a>
<dt class="shade" id="profilefield_title_15">What's On Your Mind?:</dt>
<dd id="profilefield_value_15">
$bbuserinfo[field15]
<script type="text/javascript">
<!--
vBulletin.register_control("vB_ProfilefieldEditor", "15");
//-->
</script>
</dd>
</fieldset>
</td></tr>
<!-- ########## /WHATS ON YOUR MIND ######### -->