btw, are you sure that
Code:
$vbulletin->templatecache['register'] = preg_replace('/<input type=\\\"text\\\" class=\\\"bginput\\\" name=\\\"username\\\" size=\\\"50\\\" maxlength=\\\"" \. \$GLOBALS\[\'vbulletin\'\]->options\[\'maxuserlength\'\] \. "\\\" value=\\\"\$username\\\" \/>/', '<input type=\"text\" class=\"bginput\" name=\"username\" size=\"25\" maxlength=\"$vboptions[maxuserlength]\" value=\"$username\" id=\"username\" style=\"width: 212px\" onblur=\"CheckUserName();\"/><span id=\"username_status\"></span>', $vbulletin->templatecache['register']);
will work? i think there is no such line in register template...