I have had this issue for a while now. It was occuring when I had Vista on my laptop and now I upgraded to to win7 with the same issue. When I launch MC15 and then try to play any songfile, I get a 'buffering' message and MC15 just hangs there. If I hit play a 2nd time, the program freezes. If I launch MC15, hit play once and then close it and then open it again, I get a message that the program is open in another instance. I am running NAV Version: 18.1.0.37, windows7 home premium 32bit. I have uninstalled and reinstalled MC15. windows firewall is off. I have excluded MC15 on NAV.