Comment 6 for bug 580020

I had this problem on Ubuntu 14.04 with BackInTime 1.1.2 and upon restart SSH+Encrypt worked.
I believe it is to do with the mount file system that BackInTime holds open. At some point it fails to diff I think and hence does not run the backup. Logging off and back on again kills the mount and the "re-attach" allows diff to work.
I can't confirm this is the case but it is my "best guess".