I figured out what the problem was-

When you specify an ADO source in the Report Designer, be sure the check the box for Integrated Security if you intend to attempt to change the login information via code on the aspx form that hosts the report. Also, if you attempt to change the login info, be sure NOT to call the databind method of the reportviewer.

I found this knowledge from emailing a guy who's email I got inside of the crystal developers website. Also, some of the knowledge cam e from a whitepaper in that site.

It ought to be more straightfoward...

Dave