The vBSEO issues is most likely an upgrade to PHP 5.4, which vBulletin 4 is not compatible with - especially not vBSEO.
The XCache issue could be as simple as a configuration issue, try Googling the error message and see if any of those tips help you
Fixed the SEO problem, the xCache problem is not so easy to fix, basically anytime I add the cache size as suggested by multiple sites and restart apache it does not take.