A valid .lic license-key file must already be installed on the sensor in order for the Auto/Cisco.com Update feature to function (not sure if that is the case based on your post). If the sensor has a valid license-key file installed, then the Auto/Cisco.com Update feature can be configured/enabled.
That feature (including enabling/configuring, connectivity requirements, testing, and troubleshooting) is documented on the CSC here. That same document also contains a section regarding Licensing (if you are having trouble with that as well).
