>Out of nowhere I am starting to get a lot of complaints from my customers with "a file is locked" error or "cursor is read only". I'm talking about customers that have not had an update for over 6 years and new customers so I know it's not my software. Has anyone else seen this? My guess is M$ put out an update? I'm getting this on 6 year old XP PCs and new Win 7 PCs. Any guesses? Maybe an anti-virus program? Hmmm, just realized a lot of them are running M$ Security Essentials but I can't say for sure it's all of them.

It's possible it could be a problem with a Microsoft Security Essentials update but there doesn't seem to be a lot of noise on the Internet about any recent problems, and my experience with MSE has been pretty good.

The November Patch Tuesday included the following Microsoft updates:

http://technet.microsoft.com/en-us/security/bulletin/ms13-088
http://technet.microsoft.com/en-us/security/bulletin/ms13-089
http://technet.microsoft.com/en-us/security/bulletin/ms13-090
http://technet.microsoft.com/en-us/security/bulletin/ms13-091
http://technet.microsoft.com/en-us/security/bulletin/ms13-092
http://technet.microsoft.com/en-us/security/bulletin/ms13-093
http://technet.microsoft.com/en-us/security/bulletin/ms13-094
http://technet.microsoft.com/en-us/security/bulletin/ms13-095

On a quick scan none seem to directly affect SMB file or record locking, you could check for yourself. Similarly there doesn't seem to be a lot of noise about any of these updates causing problems like that.

If you are seeing this problem across a wide variety of environments, the next step is to figure out what they have in common. The first thing would be to absolutely rule out your program itself. In addition to code updates, some applications regularly push data updates out to clients. Is it possible your application does this, and the data have somehow become corrupted or otherwise not working as expected? Or, a data file was sent with the read-only bit set?

Do you have any test or other code in your application that may have "expired" e.g. start working differently after, say, November 15 2013? What about any third-party libraries etc. you may have included?