The "You need permission to perform this action" error message in the Microsoft Windows 7 and 8 operating systems is a horrible-horrible problem.
One wonders why Microsoft does not fix it? Folders and files of which I had routine and easy access in the past are often and unexpectedly unavailable to me now that I am using Windows 7. It is totally nuts...
This video was quite helpful... https://www.youtube.com/watch?v=oC3jHe3IYXQ