Let me start off by saying that I am not a programmer. I have an IT background with computers and servers, am a lifelong gamer, and a HUGE Friday the 13th fan. (That being said, please refrain from taking jabs at me if you don't agree with the following theory)
I was playing the night of the launch, and once I logged out, I get the Database login error message now. Here we are, 72 hours later, and I've literally tried hundreds and hundreds of times (like many, many others). So, I logged into another account on my PS (my daughters), and was surprised to get in instantly. Well...I played one round, and had to quit in order to do some things. When I returned and tried to log in with her account again....boom....same login error message (repeatedly) as my account.
So here's my theory (involving the server and the dreaded "Database Login Error" message):
What if there is a glitch happening involving (certain) peoples accounts in which the system somehow believes you're STILL logged in, even though you've logged out. Naturally, the server won't allow an account to log in twice, right?