I would recommend you to check if the appliance can connect to the update servers. In the GUI, go to System Administration > Upgrade and Update Settings. Take note of the Routing Table that is used for updates (Management or Data).
Once you have the above info, go to the CLI and test the appliance to see if it has connectivity to the update/upgrade servers.
telnet
(select the interface - Management if Management Routing Table is used for updates; P1/P2 if Data is used for updates)
The sites to test are:
update-manifests.ironport.com on port 443
updates.ironport.com on port 80
upgrades.ironport.com on port 80
-Vance