I was getting this error code trying to set up gmail and I was sure I had everything entered correctly. I found the problem, I had IMAP turned off in gmail. The app uses IMAP to connect to gmail, so it won't work if IMAP is off. If you get this error, log-in to gmal.com and go to settings> Forwarding and POP/IMAP. If IMAP is off turn it on.
Hopefully this will help anyone getting this vague error message.
I use Comcast email, and I got the same error. After trying to fix it for several minutes, I realized the PS Vita was deleting the .net part of my email address when I entered it. In other words, if my email address were firstname.lastname@example.org, it only kept abc@comcast and dropped the .net at the end. I re-entered the .net, clicked into another field and made sure that the .net stayed this time before I hit submit, and my email was fixed.