Update on the Latest NIS Engine 17.7.0.12

Hi i just receive the latest update but i got some problems. On my first try of updating it, download could not complete. I restarted the computer and this time it updated perfectly fine. This has not happen once but quite frequent whenever there is update on NIS engine and IPS. I would like to know what the problem is(Update failed to complete issue). By the way i am using Norton Internet Security 2010 on Vista Home Basic.