When I tried to sign up on forum.pingendo.com, the account activation link timed out. I found a workaround, so I thought I would share it in hopes that it might help you troubleshoot.
The account activation link includes an IP address that doesn’t seem to work and doesn’t use SSL:
I replaced the IP address with forum.pingendo.com, changed http to https, and then the link worked fine.
This may be preventing users from registering.