This happens when you are using a virtual drive.(Daemon tools etc) disable it and have a go.If this does not work there is a small registry edit you must do-
to get to your registry Click the start button, then Run, then Type in regedit
at this folder HKEY_LOCAL_MACHINE/System/MountedDevices/
Right
Click the Mounted Devices folder, Click Permissions, Click Advanced,
Look under the "TYPE" header for any labels that say "Deny", if there
are any highlight and click Edit, Check Full Control and "OK". and
Viola!