Calibre crashes when I load plugin from file

I hope someone here can help me.

I open Calibre, Preferences, Plugins, Load plugin from file and the program simply exits. I can actually see the file browser window a split second before it crashes.

I've tried everything: uninstalling the program, running ccleaner and cleaning everything including the registry, installing the 32 bit version even though I have 64 bit pc, running the program from safe mode. It still crashes every time I try to load a plugin.

Thanks,
Cris