Please post back any stored code results, we are going to get this solved for you yet!

the next time the light comes on, try leaving the key in the run position with the car not running for 30 minutes, or untill the light goes out. doing this re learns the key to the car. im thinking the little resistor thing in the key has changed just a bit.

my car does the same thing if i remote start the car and then insert the key. this is because my remote starter has a spare key in the brain of the remote starter with a field wire wrapped around the ign cylinder. it sees a different value when i insert the second key and trips the light.

I did this a few days ago with both keys, left them inserted and ignition forward for well over 30 minutes each (one of them for a couple hours). Security light never went off while the key was in... it was off the next time I started the car, but has still come back on intermittently since.

One of these days I'll get scanned for stored codes and will post back those results.