I have now uninstalled Python 2 and 3 and installed them new. First Python 2 with only register extension and compile files to bytecode. After this I have made the same with Python 3. In the "Open with" menu was now "python" registered which was Python 3 (sys.version[0] from a testscript telled it me). Until this point the arguments were accepted. After this I have added the python.exe from Python 2 to the "Open with" menu. This was the point where the key got invalid. Now Python 3 is working correctly but not Python 2. Well, I can manually use now the workarround to fix it but maybe the problem can be solved with this information.