Make the following change to the LiveUpdate policy:
Policies > LiveUpdate > LiveUpdate Settings policy > Edit the policy
By default, "Use the default management server (recommended)" is checked.
You will find under the Advanced Settings, "Allow the user to manually launch LiveUpdate", is grayed out.
To enable this checkbox, go back to Server Settings: Check the box for "Use a LiveUpdate server", leaving the following checked:
"Use the default Symantec LiveUpdate server", as this setting will enable users to run LiveUpdate manually via the Internet.
"Use a specified internal LiveUpdate server" would only need to be chosen if you wish your users to manually download updates via the LiveUpdate button from your own LiveUpdate server, rather than from Symantec LiveUpdate servers.
Save and apply the policy to the relevant groups. The LiveUpdate button will now be active on SEP clients. Hence, users are now able to run LiveUpdate manually.