Error 500 when creating an AzureRMVirtualNetworkGateway using PowerShell

I am attempting to create an Azure VPN Gateway from an already created Vnet. The Vnet is created and I've got a VM inside the VNET - works great. But now I am trying to setup the P2S gateway as follows

New-AzureRmVirtualNetworkGateway -Name $GWName -ResourceGroupName $RgName `
  -Location $Locname -IpConfigurations $ipconf -GatewayType Vpn `
  -VpnType RouteBased -EnableBgp $false -GatewaySku Standard `
  -VpnClientAddressPool $VPNClientAddressPool -VpnClientRootCertificates $p2srootcert

Sadly I get this response

WARNING: The output object type of this cmdlet will be modified in a future release

Any clues a) to that this means and b) how to fix it

Thomas Lee <DoctorDNS@Gmail.Com>