I am using Windows 7. thom aqua's instructions worked for me after I managed to change the permissions to the folders in question so I could see the files to delete.
Try to undo the permission changes below after your windows media security update succeeds.
To see hidden files on Windows 7, you need to go to
Control Panel
Appearance and Personalization
Folder Options
Show hidden files and folders.
Select the View tab and under Hidden files and folders select
"Show hidden files, folders, and drives". Select Apply.
Right click On the Start Menu and select Open Windows Explorer.
Navigate to C:\Users\All Users\Application Data\Microsoft\Windows\DRM.
If you have trouble opening any of the above directories then right click on it and select properties.
In the General tab, you can remove the Read-only attribute.
In the Security tab, click Advanced to modify the special permissions.
From the displayed table, select the row with the name "Everyone" and the Apply To column
that says "Subfolders and files only". Now, press the Change Permissions button.
Again, select the same row as above and press the Edit button.
In the "Full control" row, select the Allow checkbox.
Press OK or Apply to close all the popups.
You may have to close the Windows Exporer and re-open it to see the changes.
Now, you should be able to see the files under DRM and follow the instructions given in a previous post with regards to deleting the files in the DRM directory.
Good luck. Free digital stuff from the library is great.