For example, with 14.3 RU4 the command is: regsvr32.exe "C:\Program Files (x86)\Symantec\Symantec Endpoint Protection\14.3.7393.4000.105\Bin64\vpshell2.dll"
Also verify the permission for registry key " HKLM\Software\Symantec\Symantec Endpoint Protection\AV". Permissions for Symantec: Administrators: FullControl (0xF003F) SYSTEM: FullControl (0xF003F) Users: ReadKey (0x20019) ALL APPLICATION PACKAGES: ReadKey (0x20019)
NOTE: If you are unable to change permissions directly to the AV key, try setting permissions to the Symantec Endpoint Protection key and use advanced to push those changes down the hierarchy. If it still has 'Access Denied' errors try disabling SEP Tamper protection and follow the steps again.