@method1 said:@mfah said:Could be because 2005 no longer supports the single-threaded runtime? Could you expand upon that at all? Any change from 6.0 to 2005 is a good candidate...  You can read about it here, and the official line on it here I'm guessing (and I emphasize "guessing") that if you were linking with the single-threaded CRT in version 6, any threading-related issues you may have previously had but which would not have been evident during testing/debugging may suddenly blow up in your face. I've seen it happen with other apps I've moved from 6 or 2003 to 2005 or 2008. If not, either of those pages might indicate other likely candidates.