Unexpected .htaccess redirect following signing of guestbook

It appears that after adding .php files in the RewriteRule of my .htaccess file to prevent SPAMMERS from hotlinking directly to my addentry.php file, legitimate visitors are now getting redirected to the URL (mydomain/403.shtml) specified in the RewriteRule, after getting the "Thank you" message through the success.php file, rather than back to the guestbook. I am generating the rules for the RewriteEngine via the Hot Link Protection GUI of cPanel. However, I have looked at the .htaccess file directly through a text editor. I am running Advanced Guestbook 2.3.3.

I have searched this and other forums and played with it for several hours now without success. I have confirmed that by removing the Rewrite rules, the problem goes away. I also tried adding http://127.0.0.1 as an allowable URL to no avail.

Any advice or suggestions would be greatly appreciated. Thanks.

After additional troubleshooting, it appears that the problem was due to the failure of cPanel to include "RewriteCond %{HTTP_REFERER} !^$" after the "RewriteEngine on" command in the .htaccess file. I added it manually. I have now tested it successfully several times.

Thanks just the same.