UAG Remote Desktop Gateway Server Reaching it’s maximum allowed connections
Your computer can't connect to the remote computer because the Remote Desktop Gateway server reached its maximum allowed connections. Try reconnecting later or contact your network administrator for assistance.
The following error is caused by user connections that are not closed correctly on the server side, rather than the terminal server itself. Therefore, some Forefront Network tunnels are leaked when the connection remains open. This can cause new requests to be denied when connecting to the UAG Remote Desktop Gateway Server due to the amount of concurrent connections reaching its limit. By default the maximum amount of concurrent connections is 100,000.
There are a few possible resolutions to this, one of which is to restart the Remote Desktop Gateway Service on the UAG Remote Desktop Gateway Server (This is the server that handles all the UAG requests). The service will restart and upon restart the concurrent connections currently to the UAG Remote Desktop Gateway Server will be cleared. Once this has happened you are free to restart the service and it will start accepting connections again.
Alternatively, Microsoft have also released a patch for this problem. However it doesn’t require a reboot of the server so long as the Remote Desktop Gateway Service is stopped prior to the install of the patch on the UAG Remote Desktop Gateway Server. You may also be prompted not to install it unless necessary. You can modify the maximum number of concurrent connections as part of your UAG Remote Desktop Gateway Server setup.
More information is available here: https://support.microsoft.com/en-us/kb/2649422