Have you tried:
Going into Windows Media Player 11 (I assume you want to get rid of the old NAS drive from MCE), then check that your old NAS drive isn't still being monitored (I believe this option is under library from the options menu).
Now, while you're in options, check the library settings and make sure its NOT set to delete the file when removed from the library...
Now, exit options, and change the library from music to video view.. then change the library to folder view.. delete the old NAS drive.
now press F3 click ok and let it rescan your monitored folders (make sure add anything previously deleted is checked in advanced) to put anything you may have removed from the root folder deletion.
(Adapted from a Green Button Forums post - original
here)
HTH
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