Hi Daniel,
I am actually not using any third party SEF components. I also must apologize, as I did not clarify whether I was talking about the component or the module. The CMC component works absolutely fine. The module also works perfectly fine with SEF turned OFF. The issue is when SEF is ON that it seems to have trouble passing the URL to Mailchimp.
The only thing that I have customized in my htaccess file is: RewriteCond %{REQUEST_URI} ^/index\.php/ and RewriteRule ^index.php/(.*) /$1 [R=301,L], but I have tested the module without them and still no luck.
Do you believe that the problem is with my htaccess configuration? I will try to debug a bit more and see what I can find. Any suggestions you might have would be greatly appreciated. Other than that, your script is a huge time-saver. Great work!