Well now.....actually...
It was DreamWeaver....
Not sure where and when, but DreamWeaver apparently has a nasty habit
of leaving behind tag sections, even after they don't appear on the screen anymore. So after reexamining the proc in the DLL enough, I started looking at the ASP page....that's where I found some odds and ends, one of which was screwing up the key value that I was passing to the proc. I cleaned the page up and everything works as expected.

Thank you for your time and help Craig. Sometimes it's really rough trying to track down an invible monster by oneself.

David