When setting up the pluging, one is asked to enter public and private key for the hide mail functionality. I got in the posts with email:
Warning: pack() [function.pack]: Type H: illegal hex digit in /var/www/myblog/wp-content/plugins/wp-recaptcha/recaptchalib.php on line 242
The problem is that the keys had a space at the end. Why not add a trim() for the keys in the code, since everybody will copy and paste from the site where the keys are generated.