Check the email you used to signup for Spotify. I have been having the Error Code: 3 problem for about a week. So I check my email and there is one from Spotify from the beginning of December saying they reset my password because they thought my password/account had been compromised. I reset the password and can now login error free.
I have an email (not facebook) account and this was happening with me and I had now idea what was going on. I have 2 spotify accounts (by accident) and I changed the paswords on both multiple times but it was still not letting me log in. I even made another brand new account to see if that would help. Finally, instead of entering my email, I entered my acocunt name and than it let me log in. Thank God, cause I was getting very frustrated. Hope this helps!
Found a solution, for whatever reason some idiot thought it would be smart to have separate passwords used for your online and device apps. There is a page that has a separate username that you can then get a password from. Seriously, I have never had more trouble from any software than this, soley because of just weird design decisions like this. I'm more tempted to jump ship every day.