[Bruce Edwards]

If the light is on that is a sign of a computer related fault in the system. With out being able to scan it you can not find out what is triggering the MIL. I have never run across a computer that would not scan and still make the car run.
What type of scanner are you using? Have you tried an independent shop? Some of the after market scanners may get into the computer.
Good luck and let us know what you find out.