One very common problem that I encounter every now and then with customers and when doing Windows training is the fact that remote controlling computers causes a freeze in the remote session when UAC kicks in. By default, UAC prompts for elevation on something called the secure desktop, and that effectively blocks any remote input.
This problem can be fixed by changing the necessary UAC settings. Just as a note; Never ever turn off UAC!
Configure UAC to allow for remote support by setting the following GPO settings under Computer Configuration / Policies / Administrative Templates / Windows settings / Security settings / Local policies / Security Options node:
User Account Control: Switch to the secure desktop when prompting for elevation policy = Disabled
User Account Control: Allow UIAccess application to prompt for elevation without using the secure desktop policy = Enabled