Client computers login at specified times to check and update antivirus definitions using a dedicated account configured by the administrator. One day the clients are unable to login with the account, but the server still responds to ping requests. The administrator has not made any changed. Which of the following most likely happened?
A. Group policy is blocking the connection attempts
B. The administrator account has been disabled
C. The switch port for the server has died
D. The password on the account has expired