Using a electronic flash and fisheye lens for Nikon D3000?

I have a Nikon D3000 with a Pro Optic aspherical fisheye lens and recently purchased a 7400EDF electronic flash. When I attach the flash to the camera with the fisheye lens and go to shoot on the setting mode a warning pops up and says " Flash is in TTL mode. Choose another setting or use a CPU lens ". I can't figure out what setting to use or what TTL mode is. The lens and flash are both meant for the Nikon D3000 so I have no idea what to do. Any help would be much appreciated!

Isn't that a lens that connects to the front of your kit lens? Usually those "lenses" or filters don't interfere with the TTL, but if it's actually a LENS that mounts up and auto focuses and all of that like the Bower or Vivitar fisheyes it means that the electronics in the lens don't support the i-TTL in your camera. You will have to set your flash's output manually.

TTL means "Through The Lens". When flash is set up as ttl it talks to your cameras computer and your camera will calculate how much light is needed from your flash to make a supposed to be decent brightness in your subject. Then your flash will know how much light to give when you shoot.

You are using a non-nikon brand flash that is designed for nikons. Your flash, as it is advertised should be compatible to work using nikon's ttl set up. The problem with flashes from other brands is that they are good only when they work. I've experienced different brands that were supposed to support nikons ttl but they will work on and off. Sometimes it give enought light but most of the time it will just burst the light with full power.

If you can you should return your flash and save a little more for an SB 600