After further testing, it appears that will ONLY not connect from an ASP.
It works fine from Access, from a Windows Scripting Host file, from a Delphi app, from anything except ASP.
To the extent that if you write an ActiveX wrapper in Delphi to get the connection for you, that object will also work in everything except ASP.
In other words, it's not ASP itself, it's the mere operation of connecting to Sage from within IIS.
I've tried giving the IUSR_etc. user full access to the Sage data files, but no effect.
What the hell is going on?! What's changed since version 8? Help!