I am having the same problems as you as seem to be a few others
Can you add users via PowerMessenger/users_registration.php or do you get an internal server error.
I thought it may help WA admin to pinpoint the problem if we are all breaking in the same way.
I am not getting any errors. All seems to be running properly and I can add users without any issues. My only issue, the most important, is those users not receiving the emails.