Our file would have had to have been modified by someone here
In your pp-inc.php is this line in the topmenu function
Code:
Content visible to verified customers only.
Your installation has been changed to replace {$Globals['maindir']} with {$Globals['vbulletin']} however the final part of the modification someone was trying to do was not done. uid would have to also be changed in that line to u
If you are sure you did not hack anything try uploading a clean file. I viewed the properties of the link on your site when you asked and this was what I found above.