Help: Unable to edit "Net Method"

Hi. I am new here. I did a search, but couldn’t find an existing thread regarding this. I have a problem when editing system settings: I am trying to change my “Net Method” setting from “average” to “instantaneous”, but the drop down box is grayed out. Why is this? Is this setting not possible to change once the system is added and in operation? Or is this a bug? Help would be appreciated.

The setting is a donation only feature -

Thanks. That explains it.