Symptom:

Sometimes when Remote Control notifies me that a reboot is pending, I am not able to postpone or cancel the reboot because the buttons are disabled.

Solution:

When Remote Control reboots a computer after a disconnect, a countdown dialog appears which tells you that a reboot is pending. This dialog also has three useful buttons: Reboot Now, Defer, and Cancel. In some circumstances these buttons are disabled.

This happens when more than one user is logged onto the machine, typically using Microsoft Remote Desktop Connection. The reason is that one user cannot be allowed to reboot the machine at random, because that will affect all other users without warning.