This duplicated entry error started on my local dev machine as well. I have spent 2 days with no solution.
One of the example goes like this. Drupal 6.8 > Content Type > Book > edit Then hit Save without any change. I get 90+ pages of error (pages as in print command) with Duplicated Entry warning. Every time the error starts with different entry name.
The site is acting up. I get logged out unpredictably (this is my local dev machine). FCKEditor doesn't show up for users. It doesn't show up for comment even user/1. Yes, I double-checked FCKeditor profile settings. Modules such as OG Calendar, OG Content Type Admin UI doesn't show up for config. Notification is not sending out anything, etc. It seems all the hell broke after I installed OG.
Running update.php and rebuilt permission numerous times but to no avail. I am quite freaking out. I should been writing contents for the classes starting next week.
What can I do to fix this? I feel like I should had dumped everything and started over with Drupal 5 when I saw the first sign of the problem a week ago. This is the only Drupal 6 site I have, and I never had this kind of problem with my other Drupal 5 sites. I am desperately seeking for help.
-- - Hiro
Hiroaki Honshuku, A-NO-NE Music, Greater Boston http://a-no-ne.com http://anonemusic.com