GM Passlock?

I'm trying to figure out why the Security light comes on in my 98 Astro. It
starts fine and then after a few seconds the Security light in the dash
comes on solid. It doesn't appear to affect anything. If it kills the
engine and the light blinks, it evidently indicates a problem with the key
but that doesn't appear to be the problem in my case. The only symptom is
the damned light. I believe it's Passlock II, FWIW. I've searched all over
the net and found hundreds of bypass modules but nothing on how to fix it.
I don't think a bypass would fix anything since it's not preventing
starting. Anyone have any ideas where to start or pointers to some info on
how to troubleshoot it? I'm planning on selling the van but need to get
that stoopid light fixed first.

Thanks....