Here are a couple of ideas, just off the top of my head:
Test your site with Firefox and install the addon that lets you configure your user agent so you can impersonate the Googlebot and see what it's seeing. Does it matter if the AD module is disabled when you impersonate the Googlebot, are the results the same?
I read a couple of threads when I google "302 error googlebot" that lead me to want to check if this is part of the DNN URL rewriter, so you might want to test with friendly urls on and off. Might want to post in the general configure it forum, maybe install it.
It sounds like you are analyzing your IIS log already, have a look at what pages are actually getting the 302, see if there's a trend, is it all pages it's hitting or only some of them? See if there's a trailing slash issue, and what domain name the Googlebot is hitting, with/without the www.
Good luck, do let us know what you find out!
Roberta