I'd recommend staying away from those registry optimizing programs, as they cause more trouble than they are worth. To correct the issue, do a system restore to a previous date before you installed/ran the registry optimizing program.
+1. Registry Optimizers have a really bad habit of causing more issues than they fix. It's best to simply avoid them. AFAIK, there is no evidence showing that cleaning up the registry actually helps system performance anyway.
Edit: As for actually fixing your problem, try downloading Fix WMP from The Windows Club. I've used a couple of their other utilities and found them incredibly useful.