I have the same issue with DIVI. It seems that my server is on php 5.6. I had no problem before when I was hosted on a server which was on php 5.4 and php 5.6.
Here is the error message found in the log-error.php file
PHP Warning: Cannot modify header information – headers already sent by (output started at /home/picanet/public_html/iprcenter.com/wp-content/themes/Divi-child/functions.php:1) in /home/picanet/public_html/iprcenter.com/wp-login.php on line 415
Thank you