@Yesrab 

If you are accessing the gateway GUI on the default network (or management VLAN), the message is simply reminding you that you should be using the controller and is telling you where to find it.

If you are accessing the gateway GUI from another VLAN where you don’t want clients to have access to the GUI (or see the controller information), then there are several steps you can do to prevent that. The first is to create an ACL that prevents the undesired VLAN from accessing the controller subnet. That prevents the client from accessing the controller even if the client knows the controller’s IP address. Then you need to create another ACL to prevent the undesired VLAN from accessing the Gateway Management Page. That prevents the client from accessing the gateway GUI.

Note:  Only deny the TCP protocol in the Gateway Management Page ACL.  Some gateways will deny internet access to the VLAN if all protocols are selected.

  @jra11500 

This is the way to prevent access to it

However, i think it would be better if the gateways acted like the switches do with a page like this - it doesnt even allow a login box, nor display the controller IP.  When the controller is disconnected, the switches then allow a login, which is fine.

  @Yesrab 

not quite - if the gateway is currently under control (as in, in a "connected state" in controller) - you can still log in to it but there are no options to do anything at all (not even factory reset).  Factory reset only shows up if the gateway is in a "disconnected" state.

Being able to log in but do nothing is absolutely pointless.

The switches handle it much better - no login at all if its properly connected.