Xthreads problem

[ZiNgA BuRgA]

Try deleting inc/xthreads_evalcache.php if you're getting an error related to it.
Make sure you've set the template prefix in your forum settings.

But your method of restoring isn't exactly correct.  The MyBB merge system basically just does the minimum to get posts across.  You'll generally lose all auxiliary data, including most plugin stuff.  For one, the thread field data won't be copied over.