The site is at http://ontheten.org/community
any help is very much appreciated. I did try turning off the email verification feature to no avail.
This error comes from WordPress, wpForo doesn't have such error. So problem is in WordPress or in other plugins. I'd recommend to deactivate all other plugins, if it doesn't help change theme. This issue can't be fixed from wpForo side.
Changing the theme didn't help. We found that it was the Spamshield plug in that was causing the conflict for future reference.
We found we could keep WP Spamshield active, just choose the setting that disables it for the wordpress registration form.