The user guide states that not all ports support all speeds, even if they are available in the command. And that the result of entering the command is the message you are seeing. What NIC is connecting to interface 1/0/8? I believe most of the adapters for the servers are 1Gb or higher.
I am trying to set a port speed to 100 instead of the default 1000 using the following command: 1 Enter Interface Configuration mode for port 1. console#configureconsole(config)#interface gigabitEthernet 1/0/12 Change the speed and duplex settings for the port.console(config-if-Gi1/0/1)#speed 100console(config-if-Gi1/0/1)#duplex fullconsole(config-if-Gi1/0/1)#exit But I got an error: "An invalid interface has been used for this function." Please refer to  [IMAGE]  Trying to update the port speed on the GUI also returned an error:  [IMAGE]  Could any one advise what I am doing wrong? Thank you!! 
Powerconnect M6220 Switch Unable to set port Speed