On x64, PartCover fails to load it's COM driver.
The problem of .NET/COM interop issues with different CPU types is described here: http://blogs.stonesteps.ca/showpost.asp?pid=7
in short, Console+Framework assemblies are built as AnyCPU, but the COM driver is built as Win32. Since the driver *must* be built against win32 (or rewritten for x64), only switching the .NET project build settings to x86 solves the problem.
Please fix this small issue and all x64 users will be VERY happy to use this awesome tool.