This one drives me crazy. Did you notice on the newer 06 cars that the clamshell closing bumpstops are now spring loaded. This lets the clamshell drop farther when closed to engage the latches every time. I I would have thought of it I would have asked Saleen to convert mine when I was there. I had to pull over yesterday to reclose the shell even though I could have swore that it was latched.
The sensor is likely setting this off, but it is probaby not a sensor issue. Most likely it is that the rear latches for the clamshell (1 on each side) appears closed but may not have fully locked/engaged.
A quick way to determine this is to walk to each side of the clamshell and pull up next to the door above the side scoop. You may find that one of the sides will pop up and you can try to close it again and see if the light goes out.
I would start there if it were me. Each side of the clamshell has a rubber bump stop. You can lower the bump stop to get more clearance for closing.
Hope this helps.
Leon, they are in the actual latch mechanism. Next time you have the clamshell open, look at the latches on the rear firewall of the car (not on the clamshell) and you will see the latches and the wires going to them.