I'm running Excel 2007 on WinXP SP2. 2.3GHz HP laptop, 4GB RAM.

Every now and then, when I try to open an existing .xls file, I get a "File error: data may have been lost" error message. Some of the formulae inside the file gets converted into "#N/A".

It doesn't matter how simple or complex the file is -- I've had it happen with a one-sheet file with a simple 5-10 table, and with a 50MB very complex model.

The formulae that get converted to "#N/A" are not always very complex. Sometimes they are just pointing to another cell.

No rhyme or reason why this happens. Once I correct the "#N/A" errors back into the original formulae, and save it under a different filename, it works fine.

But this problem is really making me very frustrated because I can never be sure when a file will stop working and I'll have to redo all changes since the last file I saved with a different name.

Any ideas on what's causing this and how to stop it?