I had the very same problem until I made the virtual memory portion of the hard disk larger. I changed it from 384MB - 768MB to 384MB to 1.5GB, on a 40GB HDD I did not think it would trouble me. Good news is no further problems since.
I have no idea what caused the virtual memory error because I did nothing obvious to change the running setup and had not even installed any programs prior to the warning, it just started!
Carbheatcold