I have had to uninstall RP more than once! And when I uninstalled it one time, I went into the C Drive under Programs to delete every trace of it after the uninstall. I figured that removing every piece of it would make for a cleaner reinstall.
Guess what I found? A whole other copy of Real Player hidden in the program files that was not listed on my programs list! I couldn't uninstall it because it didn't appear in the programs list. I just had to delete it all.
Then I reinstalled and everything was fine!
(Be sure you don't have DIVX in your puter - RP and it do not get along)