I had upgraded vbulletin from 4.2.0 to 4.2.2. After this upgrade there was continuous server problems and fails in cpanel services (like clamd, spamd, mysql and lfd) gets failing again and again and recovering. It seems the server load was quite high during this failures. The problem started from the next day of upgradation and till receiving these failures. None other is changed in site, expect this update. Is vbulletin 4.2.2 causes high server loads or the server needs to be updated.
vBulletin cause some additional server load, but nothing that could block your server. I suggest you to move from server OR to check on a ps -top trought SSH which services are consuming the resources.