This is something I had seen briefly before, but it's recently become a bigger problem. Code: Fatal error: Class 'ArrayObject' not found in /www/.../library/Zend/Registry.php on line 31 That class is from the SPL, which is being loaded correctly and appears in my phpinfo(); Every once in a while, that error will appear. I believe XCache is the culprit because removing it makes the issue go away. Has anyone come across this before? Is this some known XCache issue? I've always liked XCache, but what would be the recommended alternative, APC?