It looks like IDER might not be enabled. It can be disabled in several places. First enter MEBX (CTRL-P) on the client and insure SoL and IDER are enabled. Then when you access the client with Commander insure the that IDER is enabled. There will be a check box for this right next to the "Take Control" button.
Is the serial over lan feature working for you right now?
What version of Commander are you using?