Update: 28th Feb 2010 - Due to the reported problems people have been having with the existing approach below, I have created the following program for MozyHome & MozyPro. It runs in the system tray and checks various Mozy registry keys (not just the one below), and if they have been changed by Mozy, it resets them back to the values that allow Mozy to backup and restore from the network.
