The first thing I would try is reinstalling Real Player and then uninstalling it with
Revo uninstaller. [using the advanced mode]
And/Or:
Open >> My Computer >> Local Disk C >> Documents and Settings >> your User folder >> My Videos >> RealPlayer Downloads folder and delete. [or open and pick the ones you want to delete.
You can then select
Remove Missing Media in the Tools tab in Real Player.
edit: if none of that works you could try this
"unlocker" program - I have often used it with good results. It's free
