Are you trying to play country music? It appears to me that your truck is trying to tell you that you are certainly no DJ, and should probably go buy some new music.
Seriously though, I'm guessing that maybe it's trying to tell you that you have a Disc Jammed. Do you have an owner's manual? That might give you some ideas.
If you want to post some more details (make, model & year of truck), that might help. When you say the CD changer came with the truck, do you mean it was installed by Ford (or whoever) at the factory? If it's an aftermarket unit that was installed by a previous owner, the brand of changer would be good to know as well.
I know absolutely nothing about CD changers, so I'll leave it at that...