I bought my wife a N75, but the pop-up flash has never worked. Recently she was reading the manual and said that the manual says the built-in flash only works with CPU-lenses. The lens I have is an old 50/1.4 AF Nikkor. The camera pops the flash up and charges it but fails to fire; if it was a matter of incompatibility I would hope the camera would fail more gracefully. Do I need to get a different lens for the flash to work, and if so, what kind?