Finally moved to a new server. They gave me a much better rate so I stayed with them (at least for now). I let it run for a day before changing anything.

In config.inc.php I set 'SEARCH_FRIENDLY_URLS' => '1' (I was advised to set it to "0" to allow logins to work). Setting back to "1" allowed people to login, logout, and post.

So far, so good.

I tried registering a new user through the regular process a user would use. After entering the CAPTCHA Verification and clicking "Create Account" I was greeted with:

Fatal error: Uncaught ArgumentCountError: Too few arguments to function mailer::add_content(), 1 passed in /home/byzcatho/public_html/forums/scripts/adduser.inc.php on line 757 and at least 2 expected in /home/byzcatho/public_html/forums/libs/mailer.inc.php:139 Stack trace: #0 /home/byzcatho/public_html/forums/scripts/adduser.inc.php(757): mailer->add_content('REG_CONTENT3') #1 /home/byzcatho/public_html/forums/ubbthreads.php(279): page_adduser_run() #2 {main} thrown in /home/byzcatho/public_html/forums/libs/mailer.inc.php on line 139

When I login as myself, the user was created and is showing in the "Registration Queue".

Thanks for your guidance.