Hello. Since the update to Repetier-Host V2.0.0 I have a similar problem. I could figure out that the problem seems to be the Webcam window. If it is activated it is not possible to start a print or upload a gcode. The program is hanging up (no response) and I have to kill it with the task manager. If the webcam windows is not activated everything is fine. This bug is reproducible. The Host is cby BoKaPrint - Repetier