MPC 8.3 works fine for me on Win7 and 8.1, both x64. Sometimes I get the same error as you do and a sure fix for me is disabling antivirus to let MPC do the job. A couple of times machine had to be rebooted to get it working but most of the time not a problem and I never meddled with the Compatibility mode. My guess is some MPC program files get blocked by antivirus, at least on my machine it looks that way. Hope it helps.