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.