XAgent not started

When start XAgent popup indow with message
"Failed to start up the SSH-agent server.
Please refer to the "Log messages" for details"

In Log messages:

Starting the ssh-agent server...
Created a server socket.
Cannot listen on port 5435.
Deleted the server socket.
Failed to start the ssh-agent.

How to solve a problem?

Program Ver. : Xshell 5