Hello,
Please check this: How to install a license in Symantec Protection Center Small Business Edition
http://www.symantec.com/docs/TECH91894
NOTE: For a Successful License Activation, make sure you have access to the following website:
https://services-prod.symantec.com/service/IPLService.serviceagent/IPLendpoint1
Reference: Required exclusions for proxy servers to allow Symantec Endpoint Protection to connect to Symantec reputation and licensing servers
http://www.symantec.com/docs/TECH162286
Hope that helps!!