Hi Kostas.
I'm new here too. I have used a Multi Pro for years. I've had a similar problem when I try to multisample a 6x7 image at a high resolution. Maybe that's the issue? I'm running the scanner on a Mac, and after the freeze, I have to clear out several files that have become corrupted. I don't know what these files might be on your windows machine. Do you have the KM software user guide? I think it might say what files get created during scanning, and where they are. Best of luck!
ASA