The Internal Server Error is coming up because the UBB is unable to write the new files and directories to the noncgi directory as it is set with 775 permissions. It needs to be set with 777 permissions.
Unfortunately your host does not allow you to CHMOD files on your server. If you cannot get your host to allow you to change permissions on your server, I suggest you find a new host as the UBB will not work with your current permission settings.
