Use the following steps in the Symantec Web Gateway interface to check/resolve this issue.
1 On the Administration/Configuration link choose the Network tab, and click on the button to "Test Connection to Symantec Threat Center".
2. If this test fails double check your Network, Default Gateway and DNS settings.
3 If you have enabled the separate Management interface the Web Gateway will use that interface to communicate with the Symantec Threat Center.
4. To test to see if the Management interface is the issue, un-check 'Enable separate management and in-line networks", and configure your settings to use your current Monitoring or Wan/LAN settings.
5. After saving your Network configuration changes click on the button for "Test Connectivity to Symantec Threat Center", and verify that the Web Gateway is now able to communicate with the Symantec Threat Center successfully.
6. Choose the Administration/Updates link, click on the button to "Check for Updates", and verify that Web Gateway now displays the information for the Latest DB Version Available and Latest SW Version Available at the top of the screen.
7. If the Web Gateway now has proper connectivity to the Threat Center; please click on the Update button for the Web Gateway Database updates and verify that it updates to the latest available Database/Content Filter version.
5) Remove any test Blacklist entries that you were using and test your Policy again to verify that your URL/Content Filtering is now functioning correctly.