Chapter 10 Install and System Administration for FortiOS 5.0 : Central management : Configuration through FortiManager : Locking the FortiGate web-based manager
  
Locking the FortiGate web-based manager
When you use the FortiManager to manager multiple FortiGate units, a local FortiGate unit becomes locked from any configuration changes using the web-based manager for most administrators. The super_admin will still be able to make changes to the configuration; however, this is not recommended as it may cause conflicts with the FortiManager.
See Also
Global objects
Adding a FortiGate to FortiManager
Configuration through FortiManager
Firmware updates