From Xojo Documentation
Locks the Keychain.
If LockAll is True, it will lock all the Keychains on the system. Note from Apple: There is usually no need for an application to ever call Lock. Unless your application is directly responding to a user's request for a keychain to be locked, it is recommended that you leave the keychain unlocked so that the user does not have to unlock it again in another application.
If it fails, it generates a KeychainException.