Actually, I realized I didn't explain this clearly enough. Even *before* I upgraded CB but just upgraded Joomla itself from 2.5.6 to 2.5.17, the problem already started. Before that all logins were working perfectly. I figured upgrading to the latest CB might help, but it didn't. We are basically going to be deleting all users but a few and starting this particular community all over so I'm wondering now if uninstalling and reinstalling might be a better option...