As far as I can tell, this has always been an MDAC issue. I admit that changes to the code could also cause the behavior, though in fact when the issue is with the MDAC, no redirection to default.asp occurs.
If you have mods that might have changed topic.asp, I suggest that you start a topic in the Help: Mod Implementation forum.
I am connecting to the database using the default conn string in config.asp (strConnString = "driver={SQL Server};server=XXX;uid=XXX;pwd=XXX;database=XXX" '## MS SQL Server 6.x/7.x/2000 (ODBC connection)