*ponders* I'm going to speculate here, but have you set CMP to run as administrator (right click it and select run as administrator) - I don't have Win8, so I honestly can't 'walk you through it', but I wonder if this is some sort of 'permissions' thing, in that its not being 'allowed' to execute its runtime due to this ridiculous (and ineffective!) UAC rubbish Microsoft implemented from Win7 onwards.