Google Groups Redirect Loop
Apparently some people started experiencing a redirect loop when accessing Google Groups while being signed in to their Google (Apps) account. I also did and and started - well - googling for a solution. There were a couple of solution attempts documented, such as erasing your profile and clearing all your cookies, which seemed a little random and came with significant side-effects. This post is supposed to document the minimal set of changes required o get Google Groups working again (if Google does not fix the issue on their end):
Just delete all cookies for the groups.google.{com|de|<yourtld>} hostname and everything should be back to normal.