I jsut experienced this issue and was able to track down the problem on the affected appliance having lost its "name resolution" configuration. I'm not sure how or when it happened, but the name resolution was set to inherit from parent domain but no configuration was inherited.
I unchecked in herit and re-checked it and the information showed up. After saving the changes, the faults dissapeared and the GAM antimalware definitions updated normally.
NOTE: "Name Resolution" in NSM under DEVICES - DEVICES TAB - SETUP - NAME RESOLUTION