I always used to get a messige about Virtual Memory being low.
I did this and it sorted its self out. B)
Control Panel > System >Advanced (tab) > Performance Settings > Advanced (tab) > Virtual Memory change.
I set it to Min 512MB and Max 512MB.
Since I did that (In May I think) I've only had the message once and that was when my computer had been on for 3 days non stop. :P