File changed on disk.

[ZZippo]

This is still a bug that I get every 30mns or so when working with LabWindows 2017. It's very frustrating.

[Ian.W]

Could it be an archive bit on a file being set by automatic backups? Or source control doing something?

[gdargaud]

There's another possibility I've seen: a file can still be in the .prj file even though it's nowhere to be seen in the project. Open the 2 .prj files in a text editor and look for the troublesome file in them. Delete the inappropriate section.