File I/O Error Message

I have an ai file that I can not save with out getting the File I/O error message. One person suggested that this file may be corrupted since I've been bouncing back and forth between 2 different Illustrator programs. I use CS-4 at work, save as CS-3 format then continue working on it at home. I tried copying each layer to a new fresh doc. but still get the error code. Is there a way to fix this file? Both back-up files I have behave the same way.

Sorry nop, Illustrator has this inconvenient, It has some bugs and you do not have any auto save and you lose
all the work, for that reason you must to save every 30 minutes, I recommend you spend only 50% of the information in a file and 50% in another, work in either file until the error, half the error occured, again split in half and also to detect which is the corrupt entity