Try adding this right before the RewriteRule line...
RewriteCond %{REQUEST_URI} !images/nohotlink.jpg$ [NC]
It seems that your current code is creating an infinite loop. When someone is redirected to nohotlink.jpg, the hotlink protection is applied again for
that image. And again and again and again and again......
The line above should stop the hotlink protection from applying to nohotlink.jpg.
/ 
