Why can't I change my f stop on my Nikon camera with wide angel lens?

I have a Nikon D50 and I just got a new Nikon Dx AF-S Nikkor 35mm 1:1.8G lens. I'm getting a flashing " f-- " on my control panel and it won't let me change the f stop. Why not? How can I fix this problem?

ps. I've also taken off and put back on the lens but that did nothing.

You need to make sure that the CPU contacts on both the camera and lens are clean.