If there are no electronic parts then the camera will be searching for the electronic aperture signal. But it wont get any. Put the camera in manual and see what happens. It should take a photo, but you'll need to adjust the aperture on the lens itself (presuming it has an aperture ring)
Failing that, try this.. Nicked from a previous TP post.
Turn on the camera and set the aperture to your required setting now press the dof preview button and keep it in, then press in the button you use to remove the lens and give the lens a half twist to break the electrical connection, now turn off the camera and you can also release the dof preview button.
Put the extension tubes on the camera along with the lens and you can now use the lens with the aperture you slected. It will still show as f/00 on the screen as the lens has no electrical connection with the camera but the aperture will be retained by the lens.