Você precisa ativar uma configuração de Diretiva de Grupo e / ou fazer o download de um hotfix:
However, in order for this to work properly in scenarios that prompt for elevation (i.e. UAC prompt), you have to enable a certain group policy:
User Account Control: Allow UIAccess applications to prompt for elevation without using the secure desktop
What this will do is it will enable Remote Assistance to show the UAC prompt on the user’s desktop, as opposed to the secure desktop. If you don’t enable this, the user being helped (call him novice) will get the prompt on his local machine – so the expert cannot interact with it since RA will only remote out the user’s desktop. At that point, the novice may not know what to do with it, and/or he may not have the administrator password. So it is important that you enable this group policy in order to have the UAC prompt show up in the user’s desktop and have RA remote out this dialog to the expert’s machine.