PayPal auto-return preventing registration

I’ve generated buttons for two membership levels. After visitors submit payment via Paypal, they’re being returned to a blank white page with the auto-return URL plus a long string of characters.

http://www.canadiansabroad.com/?s2member_register=fnhlOmIxMGU2ODM0YTg4OTZlNTE3ODg3NDNhNWEwZDZmMzk1fLDdtfC34LrVg6PP4dLqqb2WmZLB19ToreTPid3Pq8vB5tbVf9-8vdLO2t_GuZ3HqqzSwqpaZXvwhaFuuqSZvtrNsndts5tOqZaTpp6jsmF4iLF-Y47Dhnxs4YqifuLP2U6U0ejS2q2no5OUsNTh1q6g04_mqnaQyqyVolGwdpLhqZqkiopujntxoIh4WA#www.canadiansabroad.com

Payment is triggering email confirmation to customers prompting them to follow the link to select a username and password, however the link also directs to the same blank page (above).

When I manually enter the registration URL (without additional characters), the registration page comes up fine. http://www.canadiansabroad.com/wp-login.php?action=register

I’ve set my auto return url in paypal, enabled payment data transfer and set my identity token.

I’ve also confirmed that loopbacks are enabled on my server.

Ran the server diagnostic tool and it said that php module mcrypt was not installed but have since installed it and still no luck getting the registration page to come up after visitors submit payment via paypal.

Any help would be GREATLY appreciated! Many thanks.