I got above mentioned error while installing discourse on aws ec2. The problem was with my SES smtp password ( AmQ/22sNDN2Bg5vS+zH3IDfy+lfmF3OgGg/CnsAZMg90 ). Later I changed the password to one without any special characters and it worked. I am not sure its a bug or discourse wont encourage password with special characters. I thought I have to inform.