Bruce, maybe you could just talk to the person who you think posted the note (civilly of course) and ask them why they were upset enough to post it, and try to resolve the issue. I would ask to meet with this person outside the dojo, maybe for a beer or something. Make it friendly, try to resolve this in a cooperative manner.
Best wishes on this.
Oh, btw, I think the forums are an excellent education tool and a great way to get many different opinions from a wide range of folks. I wouldn't stop posting, but always remember they could be viewed by anyone.