Subscription for membership goes into a loop

A prospective client has let me know that signing up for a product is producing an error. Previously this has worked. However, I did attempt to move the whole WP site last weekend but had to back out of it. Whether that's changed anything I'm not sure.

Here's what happens, they get to the subscription page, click through, put in their login details and click register user and then it times out trying to get to the protected page?! It never went to the PayPal payment screen. So I checked the payment gateway and nothing has changed. I then tried another browser (Chrome) and go a message saying "The webpage at resulted in too many redirects. Clearing your cookies for this site or allowing third-party cookies may fix the problem. If not, it is possible a server configuration issue and not a problem with your computer."

Any ideas?