As mentioned before, PartCover fails on a x64 machine. The main reason is the Profiler API PartCover.CorDriver.dll
Instead of setting the target to x86, leave it on AnyCPU and provide a win32 and x64 Version of PartCover.CorDriver.dll and register both of them.
It is best when the framework itself registers these components not the setup utility. That makes it possible to xcopy deploy PartCover.
You must compile and provide a PartCover.CorDriverx86.dll and PartCover.CorDriverx64.dll and register both as COM Components