.htaccess/hot linking images problem

I have set up the .htaccess to block the use of images from my website and replaces the image with a "special" one I created. It works perfectly....but I have a user at a message board, which I have hosted there, getting the special image while visiting the board. He is the only person complaining of this. What could be his/my problem?

I set mine up like this:

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://your_domain.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.your_domain.com/.*$ [NC]
RewriteRule .*\.(gif|GIF|jpg|JPG)$ http://your_server.com/bad.gif [R]

HTTP_REFERRER is unreliable at best. It depends on information given to it from the browser. Not all browsers either give that information or give it corrrectly. Find out what browser and version they are using.

He is using IE 6.