I'm no expert, but it sounds like your SWAP FILE problem. A year ago, I experienced a simular problem. My problem was my sawp file was set to my 1Gig hard drive and the project's temp file was using all the HD space. When it came time to save the project, it had nowhere to save to. Check under PREFERENCE and see where your Swap file is set to. Also check to see how big the project file is. Personaly, I still use a PhotoShop golden rule; "A project size open is 3x it's close size. Solution is set your swap file the another HD and buy more RAM.