And once again I wasted a good hour trying out all the suggestions for how to fix the Permission denied error on Windows 7 when trying to drag and drop an assembly into the pre-.Net 4.0 assembly cache. I can assure you that starting the Explorer with elevation, from an elevated command shell, etc all does nothing. My user account is a domain account that is also a local administrator. The only thing that helped in the end was adding the domain user to the list of users with permission to Act as part of the operating system.