I'd google check on the exact wording of the error to see where it comes from. It could be Cubase, Windows or from the programming language (or package used to program Cubase) which, last time I looked was C++, which might give you a clue as to what is causing this.
A quick idea: How full is your C drive? I did notice that Cubase chucks all the backups there and it gets full mighty quickly.
From Cubase6 run the Project assistant and, if you have a spare drive or partition, direct the backup/save files somewhere else.
Success is round the corner. It's also round the bend.