Error 400 for an disabled account

Every few minutes (5-10) I get an error message in the Calendar app saying "Error 400" for my att.net account. However, this account is turned off for Calendar. The only calendar account I use is iCloud; the other ones for gmail, my school gmail address, and att.net are all turned off. I only get the error 400 message for att.net. It is really frustrating to have my calendar always bouncing in the dock telling me there is an error because it cannot reach something that is turned off. Thanks in advance for any suggestions.