Donation returning 404

Hi there,

I am trying to get a donation form going but it just keeps returning a 404 after a successful donation.

Here are the things I’ve done:

– Flushed permalinks.
– Set the custom page for a successful donation.
– Cleared the application cache
– Cleared the website cache, (utilising W3TC plugin).

Thanks,

Gabe.

The page I need help with: [log in to see the link]