Unexpected File Format Error

Just had this happen to me. Parts have become corrupt, even the backup is corrupt. Last thing I did was rename the files using SWX Explorer. SP3. Windows2003 with the latest. No viruses.
I've lost the work, am hating life right now. Backup also doesn't open. Only clue may be that it was renaming over the network...
Any advice? I've sent the file already to my VAR to try to fix.

I've had the exact same problem. Our files are on a server but the backups are local. Typically the last thing I do is save and close all and the next time I check the files they won't open and I get the 'Unexpected File Format' error. Then I go to my local backup directory and my backups are corrupt too. I've been keeping 5 levels of backup so I can usually recover something, though I often lose several hours of work.
I've sent some corrupt files to our VAR and they've forwarded them to SolidWorks Development. Our VAR has told us that this type of corruption is often caused by a bad network.
There have been recent posts on this problem and its various permutations. I honestly don't know if this is a SW issue, a SP issue, or a computer/network issue. I'd like to find out though.

Hey thanks for the reply.
I don't understand how my company can keep using this software if this might happen so often!

Wouldn't happen to be running an early version of Win200 svr and WinXP by any chance?
We had some serious file corruption problems that had something to do with this when XP first came out. The IT guy was stoked when he found some technet article (sound right?) about some MS patch that fixed it...
Hope it helps!

Try deleting all the temporary files ( ~*.*) files left over after a crash. This seems to be related to the problem