Thanks Mike. I appreciate that.

I can't speak to why your RDP server is not responding within the ~15 seconds that Guacamole waits for connections to be established. If the server was just started, it likely simply isn't ready to accept RDP connections at the time the attempt was made.

How can we make sure that RDP server isn't ready to accept RDP connections ?

This is not only happening if server was just started but if user connects once and again try to reconnect after an hour ( any time ...)

Regards, 
Amarjeet Singh

On Mon, Mar 12, 2018 at 8:44 AM, Mike Jumper <mike.jumper@guac-dev.org> wrote:
On Fri, Mar 9, 2018 at 5:19 AM, Amarjeet Singh <amarjeetxc@gmail.com> wrote:
...

Is it really because of the Network too slow  ? [  How could we make sure that it is really because of network too slow.  ]


No, but as the error message says, that is the typical cause. In this case, it's more likely that your RDP server is not responding before Guacamole gives up.

or 

Is it taking time to communicate to AD for authentication ?


I can't speak to why your RDP server is not responding within the ~15 seconds that Guacamole waits for connections to be established. If the server was just started, it likely simply isn't ready to accept RDP connections at the time the attempt was made.

- Mike