Sounds like your hard drive is getting full. Windows creates a swap file on your hard disk for virtual memory, and it needs a certain amount of space for it. If you collect too many files, Windows won't have enough room for the swap file any more and you'll get that error.

The easiest way to fix this, is just delete some files off your hard drive. Either look for old files you don't need any more and delete them, or back them up first and delete them.