I posted an answer in this discussion.
When I went to Edit my answer, I got this error and was unable to save the edit.
Thanks for flagging this.
I see this error when content is cut and pasted from other webpages etc. Often there's hidden formatting/HTML code in the pasted content that our forum engine doesn't like. Current solution is to paste the content into a plain text editor, like Notepad and then cut and paste it from Notepad.
Hope that helps?
Also, looks like you are on your way towards one of our forum awards. :-)