iTunes Won't Open

Everytime I click on my iTunes program to start, I recieve the message "The folder 'iTunes' is on a locked disk or you do not have write permissions for this folder". This message has NEVER shown up on my computer before. I can't get on to iTunes at all nor use my iPod 4th Generation because I forgot a password and I was simply going to restore my iPod, but now I can't even do that.

Please, someone help me.