Most likely the light is burned out on your deactivation switch. Do a search on Google and you'll find several sites that talk about replacing the light (from Radio shack) for a couple bucks and it solved the problem.
That was with a quick search on Google. I'm pretty sure someone on here has already wrote a "How to" for this. I'll look for you.
Here's a site I found that talked about "code 27"
Hope this helps..
Here's one from RPS..