Its a server issue. Wait for some time until they resolve.
It seems like you have a conflict and possibly you've mixed up files. Download a clean copy of mybb and upload that removing the old files. (don't overwrite /inc/config.php and inc/settings.php)
The url to usercp is supposed to be:
http://www.fifago.com/demo/forum/usercp.php
But trying to go to the above link takes me to
http://www.fifago.com/forum/usercp where I see error related to vbulletin
This is the MyBB Support forums, not the forum to get support with a copy of vBulletin.