I imported a 5.9 million post database from vBulletin 3.8. The import went smoothly, but I've started to have some trouble rebuilding XenForo's caches. I first tried the rebuilding the caches immediately after the import, but that stopped with a nondescript error. I decided to skip the rest of the rebuild process at the time but have now returned to find the "Rebuild Cache" features do not appear to be working. Clicking on any of the "Rebuild Now" buttons takes me to the "Rebuilding..." page, which then immediately directs me back to the main Rebuild Cache page. This occurs with all of the cache rebuild options. I've checked the server's error logs but came up empty handed. Any ideas on what could be wrong?