I have multiple accounts active on my phone. I started by using my custom domain Google account, because it had my contacts. When I got on Google+, I couldn't use that account, so I had to link my normal Gmail account with my phone. And when I added my YouTube account, it threw that account on there too.
Now, in intervals that range from every few days to every few minutes, i get a notification that says "Sign In error with account (account name here)", then asks me to enter a capcha-like entry (enter letters of distorted words).
It usually happens to the standard Google account (@gmail.com), but has happened with all three at one time or another. Anyone know why this would be happening?