Microsoft recently made available a hotfix to address an issue where Remote Assistance connections to remote DirectAccess clients fails. The issue occurs specifically when Windows 7 clients connect to a Windows Server 2012 DirectAccess server using the IP-HTTPS IPv6 transition protocol. In this scenario, DirectAccess clients are assigned a Unique Local IPv6 Address (ULA) using the prefix FD00::/8 for which Remote Assistance service would not listen on. If you are planning to support Windows 7 clients on your Windows Server 2012/R2 DirectAccess server and you need Remote Assistance functionality, you’ll definitely want to ensure that this hotfix is applied to all of your Windows 7 DirectAccess clients.
For more information and to download the hotfix, please refer to Microsoft Knowledge Base article KB2912883.