The remote desktop gateway server is temporarily unavailable

Hi,

I publish my RemoteApp program to RDWeb. I can access RDWeb and open it without any problem from any computer within the same domain. If I would like to access the same RDWeb from another domain, I can still open the RDWeb page, but when I open any program, I will get the error:

"Your computer cannot connect to the remote computer because the Remote Desktop Gateway server is temporarily unavailable".

I check the Remote Desktop Gateway service is running.

Any idea,

Thanks,