Membership Plugin Signup form redirect loop

When a user fills out Step 1 of the membership signup form page and hits next, it will take them to the next page for a split second and then bounce them back to Step 1. The user is created within wordpress so of course if they fill it out with the same information they see ‘User ID already taken’.

Please help me with this, I have a feeling it requires a code fix as I have eliminated permissions issues (yes a stranger has access to the signup page etc). I bought this plugin almost a month ago and have had nothing but issues (I realize this could be owing to my individual wp config) but really don’t want to switch to another membership plugin and start all over again.

Thanks in advance.