You are missing the IF commands and some other key user information. Please refer to my example below (which you can copy+paste into your template).
PHP Code:
<if condition="$show['member']">
<td class="vbmenu_control"><a href="login.php?$session[sessionurl]do=logout&logouthash=$bbuserinfo[logouthash]" onclick="return log_out()">$vbphrase[log_out]</a></td>
</if>
Please let me know if this works,
Thank you