I get 'Internal Server Error 500' all the time. Persmissions are correct. What must be done?

Some windows based servers have own rules to work with .htaccess files, so it can be recognized wrongly.

Try to delete this file, and run Form Processor Pro. After finishing Initial Installation Script you can deny web-access to needed files via your cpanel.

Also this error can happen because of SMTP server.

Comment email actions in config.php and try to run your form. If form works ok without email actions then check your email templates.