It's a really odd problem this. Comments from the web UI don't work, and yet if I trace the SQL using the Profile, and copy the SQL being executed, and run than explicitly in Query Analyzer it works. What's changed? Well, I'm using dotText and have the comment spam triggers from here. This used the blacklist by Jay Allen (updated daily), who recently took it down, and my blacklist was just populated with his web page explaining his take down - something I didn't notice since I was away. I've repopulated the blacklist, but since the original replacement, comments don't work. At all.
Anyone with ideas please mail me - you can find my email address on the ipona website.