Have you set up the environment correctly? Check below:
https://help.symantec.com/cs/DCS6.7/DCS6_7/v94987005_v110163010/Setting-up-the-VMware-NSX-environment-for-Data-Center-Security:-Server%7CSymantec%EF%BF%BD-Data-Center-Security:-Server-Monitoring-Edition-and-Server-Advanced-6.7-6.7-MP1-6.7-MP2-6.7-MP3?locale=EN_US
https://help.symantec.com/cs/DCS_INSTALLER_1_0/DCS_INSTALLER_1_0/v93786255_v105294950/Deploying-Security-Virtual-Appliance-in-VMware-NSX-environment%7CSymantec%EF%BF%BD-Data-Center-Security-Installation-Guide?locale=EN_US
Thanks!