** UPDATE: I fixed the problem by checking all the comment dates in mySQL, and found the problem was a comment year of “2010”.
I am also having this problem on one of my WordPress installs. Version 2.0.2. No spam plugins installed (only 2 were activated, and I even disabled them). Cleared cookies & cache. Server date & time are correct, local PC date/time is correct (same timezone as server, same exact time). I even rebooted the server. Monitoring the apache logs gives no error. I’m not sure when this started because this is my dev sever. My production server (running on the same physical server) does not have this problem.
** I just had someone else in another location test the site, and they could post a comment. I’ve tried using both IE & FireFox. Same error. Tried logging in as admin, and posting, as well as posting as a guest. Same error. I can post comments to my production site, though. This is very baffling.