Resolution:
The Broker Admin page in the GridServer Administration Tool has an action that enables you to log in to other Managers to modify other Engines or perform other administrative tasks. This page makes an HTTP connection to the Administration Tool on the other Manager.

If you use SSL for connections to Administration Tools and you have either disabled regular HTTP connections or have blocked the ports to use regular HTTP connections, this feature will not work. To administer other Managers, you will need to open regular HTTP connections to it, or manually open a connection to the Manager's SSL port to log in to its Administration Tool.