For me, the solution to the problem wasn’t mentioned anywhere in the forums.
My problem was with my Authentication Unique Keys.
In the config.php file, in the Authentication Unique Keys section where you are supposed to define unique phrases, I had copied and pasted phrases from a random wikipedia entry. I reread what I had copied, and it turns out that there were all kinds of punctuation marks (.,:; etc…). I removed all those and left only text and spaces and that solved my problem.
