I got my mp3 player back in January and haven’t had any problems with it. Then, one day, I plugged it into my friend’s computer and put some of his iTunes stuff on there, and it worked just fine. But then problems started happening. Songs that I had put on there wouldn’t show up, things like that. But it wasn’t that big of a deal. But now, something really bad is happening. I can delete songs just fine, but my computer won’t let me add anything else. I use Windows Media Player, and when I try to sync a song, it gives the a message with something about “cannot find device’s certificate”. I get a similar message from RealPlayer and from this audiobook software called Overdrive Media Console. What’s wrong with my player and how can I fix it?