When you try to refresh Network Service in VMM 2012 R2 and particularly Network Service for Windows Server Gateway you may received the following error:
Unable to connect to the network service. Check connection string and network connectivity. Error Execution of Microsoft.SystemCenter.NetworkService::OpenDeviceConnectionEx on yje configuration provider <GUID> failed. Detailed exception: Microsoft.Carmine.WSManWrappers.WSManProviderException: A Hardware Management error has occurred trying to contact server hyperv.contoso.com :w:InternalError:HRESULT 0x8033381e8:The WS-Management service cannot process the request. This service has exceeded its maximum concurrent operations per user allowed for plugin “WMI Provider”. Tretry the request later or raise the Maximum Operations per User quota. .
WinRM: URL: [http://hyperv.contoso.com:5985]. Verb: [ENUMERATE].
[http://schemas.microsoft.com/wbem/wsman/1/wmi/root/virtualization/v2/Msvm_VirtualSystemManagementService]. Filter 
One solution to this issue is to restart the WMI service on the mentioned Hyper-V host.
If still there are issues restart of the Hyper-V host can also be solution.