Since the upgrade of my system to Ubuntu 16.04.1 LTS with KDE I'm having the same problem (Error while adding the file monitor.). Since I try to automatically save the screenshots to my home folder and the home folder is encrypted, I suspect the encrypted home folder as cause of the problem.
Since the upgrade of my system to Ubuntu 16.04.1 LTS with KDE I'm having the same problem (Error while adding the file monitor.). Since I try to automatically save the screenshots to my home folder and the home folder is encrypted, I suspect the encrypted home folder as cause of the problem.
The debug ouput is unsuspicious without warnings.