These are some more files that need to be unblocked
/components/com_dtregister/success.php
/components/com_dtregister/assets/js/calendar/wdCalendar_lang_US.php
/components/com_dtregister/assets/js/dt_jquery.js
components/com_dtregister/captchasecurityimages.php
Also, if you are running latest version of admintools, you'll have to ensure that "automatic compression of static resources" and " Set default expiration time to 1 hour
" are set to off.