I am having the same problem. After signing up from a different account, I got the following message:
Thank you for joining us!
Please complete your registration by visiting the following link:
As you can see there is no link. I went to PAGES / FORM SETTINGS but I cannot find where to add any other information. In REGISTRATION PAGE (Mandatory) I have the address of my sales page and in Membership Payment/Join Page (Mandatory): I have the address of another sales page similar to the other one. Those seem to be working fine and I do not think they should be the pages where the user creates their username.
There are a lot of optional pages which I assume should not be the ones causing the problem. Could you let me know what is wrong? THanks,