Once you have gotten that message you are out of luck with that file. What this means is your hard drive must be full. REvit creates a swap file while you are working and it grows and grows, eating up disc space, you should make sure before you work on a revit job that you have a min. 5 gig freespace on your computer. I learned this the hardway myself. Even after deleting everything I could, I was still unable to save. It is a bug in my opinion, non the less. There is one option. If you leave the file open, clean up your hardrive so you have enough space(ie 5 gigs) then you can try opening a copy of your file in the same session and copy paste, then save. I don't know if this will work.
