On no left space on device no warning/message is shown, the authentication still fail and you'll see the public maps. An internal server error message would be a better message
On user not found we show a page with message "An error occurred: Username "dummy" does not exist."
On invalid password we show a page with message "An error occurred: Invalid user username/password"
A message "Invalid user username/password" in an alert (or html) would be better...