If there is no internet connection from SEPM [ie. secure environment] the errors are expected and by design.
To verify, try browsing to "http://securityresponse.symantec.com/avcenter/venc/auto/index/indexA.html" and check for the return of any text.
Check if there is a proxy in the environment.
To check the settings,
1. Click “Tools”
2. Click “Internet options”
3. Click “Connections”
4. Click on the button “Lan settings”
5. Verify the “Proxy Server” setting section. It should be blank and the check box unchecked if there is no proxy present.
Verify the settings on the Symantec Endpoint Protection Manager,
1.
Click on “Admin”
2. Click on the “Server” bar.
3. Right click on the name of the server that is being checked and select “Edit Properties”.
4. Click on the “Proxy Server” tab.
Verify the that the settings match those of IE and then click on the “OK” button