Probable Reason for antivirus signature/ definition update failure

• Their was no connection available between workstation and update server.

• IP address of the update server is blocked on firewall  that is present between antivirus and update server.

• License of the antivirus is expired.

• Some other antivirus is already installed on the workstation that is not allowing the antivirus to update ( the one which you are trying to update).

• If your organization has some proxy that filter all outbound traffics then it may be possible that your antivirus proxy setting is not configured properly.

• Some malware is their that is creating some problem in update process.

• Workstation or system was in shutdown state.