Have you tried checking to ensure that System and Administrator accounts have the proper permissions on the drive?
Check out this KB article ->
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q315270&fr=1
It's old (from December of 2007), but it might help you out. It applied to XP but you might be able to still fix your problems.
You might also want to try running an elevated command prompt as administrator and run the following command if you have the Windows Audio File System installed:
sc config afs start= disabled
Read here for more info -> http://social.technet.microsoft.com/Forums/en-US/w7itproperf/thread/c5cfe9d0-e3d8-4625-85b1-3efdf04cd1a0