There is a thread about two weeks old titled "Service Theft System"
There were 18 of us who posted asking about the message.
12 of us had 2000 SSEi'*, 1 had a 2001 SSEi, 1 had a 1995 SSEi, 4 didn't identify what car they had.
2 people replaced the Theft System module, and that did not fix the problem.
2 also got the Service Stability message.
None of us has yet reported fixing the problem.
I have a theory that these messages relate to a slightly tired battery. My '98 Corvette started giving me strange messages on cold days when it was 5 years old. It cost me $70 to have Chevy tell me that the battery was getting weak. A $70 DieHard from Sears made all the messages go away.
Now the really interesting part. I have never seen the battery on my SSEi. I looked up on the Sears website to see what DieHard it will take.... and the Website says Sears doesn't stock a battery for the 2000 SSEi.... Huh?
Anyway, I'm not going to let the dealer touch the electronics on my SSEi until I've tried replacing the battery.