RuleManager: Failed to import rules from file

In the Netcam Studio X Console log the mentioned error popped up:

It turned out that the listet file Rules.xml was empty (or only contained white space).
I copied the file from another Computer with netcam-studio installation, which fixed the problem (after a PC restart).
What I wonder about is how could it happen that from one day to the next this file was all of a sudden empty. It is very unlikely that somebody manipulated the file manually.
Does any body have an idea what could lead to a modification of the file Rules.xml (all the other files in the folder where unchanged)?