While upgrading, applying service packs or adding ISV solutions sometimes you want to prevent users from accessing a specific terminal server. Here’s how:
Open a command prompt and enter c:change logon /disable.
to restore access enter C:change logon /enable in a command prompt.
[H.T. to Rob Mitchell of I.B.I.S.]
Weekly Dynamic: Disable Login on Terminal Server
Install, Upgrade & AdminTips & Hidden Features
Archived post from 2011. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.