That it's a common mistake? Because I do that often. SO often, in fact, that it's gotten to the point that I'm paranoid about it. Unfortunately paranoia hasn't stopped me from making that mistake.
It can really cause problems. Many years ago I posted a reply on this board in which I made that error.... the rebuttal was severe. I tried pointing out that it was a simply an error and that a simple rereading of the entire paragraph, (putting it in context), made it quite apparent and easy to see that the word 'not' should have been there but too late.... the replier wouldn't accept it. It was heated. So what I'm saying is - good catch! - JamesJM