My Visual Studio 2015 project would not publish via FTP after it worked for almost a year. It is .NET Framework 4.5.2.
After a compiler update a couple of weeks ago, I would sometimes have to try publishing twice before it would update. Last night after a Windows Update, it wouldn't publish at all.
Solution:
Hope this helps someone with the same problem.
I uninstalled compiler 2.6.1 and installed 2.0.1 (compatible with .NET 4.5.2) and was able to publish via FTP without any problems or errors.