bloody avg antivirus for windows today alerted me that itunes program files (i tunesminiplayer.dll) was a virus. After much uninstalling and regedit found out it was avg mistake.. just need to do a update virus definition if u see the error..
read more from here...

http://www.softsailor.com/news/5947-itunes...unes-virus.html

Right after AVG detected a trojan horse or virus in iTunes, people start getting an error and need to download iTunes again. The error is “itunesminiplayer.dll failed to register” and currently we don’t have an official fix for this, but it seems reinstalling iTunes fixes it.

I didn’t get this error, but I think it’s a possibility that AVG breaks iTunes by deleting or putting into quarantine some files, like iTunes.dll or iTunesRegistry.dll.

Try to add an exception to AVG so it won’t affect iTunes anymore and then take out of quarantine those files or reinstall the software.