To avoid above warning, please follow below steps:
1) Download/ take a copy of the voyenceca.crt from
$VOYENCE_HOME/conf/CA of AS to Client machine.
2) On Client machine:
Open Control Panel -> Java -> Security - Manage Certificates -> Import, provide the path of file downloaded in step 1. Close the window.
3) Now delete the browsing history of IE, and navigate to
https://<NCM_ServerName>, below page would come up without initial security warning.