Monitoring ESXi v5

Hello,

Is it really impossible to monitor VMware ESXi vSphere 5 ? Can you tell me if the problem below can be resolved ?

I tried and when I enter the credential (via "Edit Monitor") I have errors :

"Please crosscheck whether 1) Host server is running properly 2) Host server port is accessible. If the server is behind a Firewall and if not accessible, then open the port by configuring firewall."

So I don't receive the data (CPU usage, Memory, disk , etc.) in App Manager.

For information on the server where App Manager is installed, I have no issue to connect to my ESXi with the vSphere Client. There is no Firewall and servers are in the same network LAN.

Thanks in advance for your help.