Registering not working on membership plugin

Hi there, I spotted that someone else on the forum also got the message "Sorry, your signup request has failed. Try again." And I left a comment, but I'm not sure it is exactly the same problem. When testing and creating an account
I usually use my own membership buttons but, as this was not working, I just added the standard shortcode - both give the same message - with the person signing in only becoming a member of the site and NOT a member of the Membership plugin.
Obviously not being able to register is a big deal, and not too sure where to start looking for the problem.
All the best,