automatic security scan has problem

I just upgraded to the latest version 18.1.0.37 of NIS.  Whenever it starts the idle time auto scan, I get a popup message of security scan  "an encountered.and scan cannot proceed.  possible reason: no security definition are available to run a scan"  quit  or download.  Download doesn't work.  I am able to run a scan manually and the definitions are up to date.  Any help would be appreciated