I just had a look and unfortunately get the same issue (device write fail on the GetRemoteMmiv2Focus call)
var test = _device.GetRemoteMmiv2Focus(type: RemoteMmiType.MMI_TYPE_BUSYLIGHT, actions: new List<RemoteMmiInput>(), priority: RemoteMmiPriority.MMI_PRIORITY_NONE);
Can I call down to the unmanaged Dll somehow?
I installed the browser SDK / chrome extension and seem to be having the same issues. Onhold/ring etc work fine but when I try to setMMIFocus or setRemoteMmiLightAction I get "FileNotAccessible" error: 8
CommandError : Command setremotemmilightaction failed with error message setremotemmilightaction and details: