When Symantec Critical System Protection 5.2.9 (CSP) is installed and the Windows Core policy is applied, installation of Symantec Endpoint Protection 12.1 RU3 (SEP) may fail.
The CSP rule set is causing the SEP installation to fail.
You must make additional exceptions for Windows Server 2003 (32-bit) and Windows XP (32-bit):
Note: The default installation path displays below. If your clients have a custom installation path, use that instead.