I had an issue when I had one ESX4 server that had some slightly tweaked routing. This resulted in the service console not working via vCenter. It would error giving an MKS error on port 903. This is the mouse, keyboard, and something beginning with S port used with the service console. I also could connect to it via ‘telnet IPADDR 903’ so something weird was happeing. After discounting the firewalls, I googled and found a fix.
Here it is:
Here’s one thing you could try:
– ssh to your ESX box
– add the following to /etc/vmware/config:


– try reconnecting

Hopefully that should allow you to work around the problem.

this was taken from: