Why am I being automatically logged out?

This occurs if you have signed in with your account details from another system or web browser. The session limit is to prevent unauthorized access to your account.

The entire message displayed is:
"You have been automatically logged out. Someone else has logged in with your username and password and the maximum number of 1 simultaneous sessions was exceeded. This may indicate that your account has been compromised or that account sharing is not allowed on this site. Please contact the site administrator if you suspect your account has been compromised."