this button:
Loading Image
has this link to :
http://desuforum.com/member.php?action=profile&uid=
it can be fixed by going into your header_welcomeblock_member templates and changing /member.php?action=profile&uid=(whatever you have here) to /member.php?action=profile&uid={$mybb->user['uid']}
or you could remove the &uid= part completely and just have:
/member.php?action=profile
idk, what you have now still works, but it isn't right :s