Modifying Settings on a device with Set-WMIInstance

Hi all,

I am trying to modify a paramter from a FC HBA on a WS2012 host through powershell:

Set-WmiInstance -Path '\\<HOSTNAME>\root\virtualization\v2:Msvm_ExternalFcPort.CreationClassName="Msvm_ExternalFcPort",DeviceID="Microsoft:<GUID>",SystemCreationClassName="Msvm_ComputerSystem",SystemName="<Hostname>"'  -Namespace "root\virtualization\v2" -Class msvm_externalfcport -Argument @{SupportedMaximumTransmissionUnit=131072}

But I got error:

operation is not valid due to the current state of the object.

I am not an PS expert so my question is how I can modify the property "SupportedMaximumTransmissionUnit"?

Thanks for help in advance,

Markus