This simply means that either you cant ping the server or telnet it at 4750. see if you have connectivity via hostname and IP both. Can you perform tests from the appsevrer using the hostname?
Hey Malek, You might see this error when the server islisted in DNS but is down or the agent is not running.
Make sure Bladelogic service is running on the server,Check the DNS servers for entries for such servers. Make sure they point to the right IP Address,Make sure no firewall rules prevent access to TCP port 4750, Restart Bladelogic Agent Service on the serve, at a last resource restart the server.