Fundraising Plugin

I have installed the Fundraising Plugin and have set up a simple fundraising page with a $500 goal.

I've configured the Paypal IPN to http://www.shagstarter.com/wp-admin/admin-ajax.php?action=wdf-ipn-return-paypal

When I check out with Paypal the donation goes through, but this page is a 404:

http://www.shagstarter.com/fundraisers/shags-40th-birthday-present/thanks

And the donation is not logged as part of the Fundraiser.

I really need to get this working today, please advise, thanks!