When Rapid release AV definition download mode (mode==2) is selected in the configuration of the Symantec Messaging Gateway for Service Providers (SMGSP), sometimes jlu-controller logs show download error codes 6, 18 or 28.
(ERROR:11511.2968156816):  Failed to install the Rapid Response AV definitions.
(ERROR:11511.2968156816):  Download failed with error 18. URL: http://definitions.symantec.com/defs/rapidrelease/ennlu64.lin
These errors can be safely ignored as they are intermittent network/server issues. JLU will download the AV definitions per the next time on the schedule.
A possible solution is to increase the "jluTimeoutMinutes" attribute in the bmiconfig.xml. This would only resolve the issue if the download is slow due to poor network performance.