PIP on a Multi NIC VM

I'm trying to fix a Public IP address on a VM that has two NICs. But PS returns the following when i run:-

PS C:\> Get-AzureVM -ServiceName AZUREVM -Name AZUREVM | Set-AzurePublicIP -PublicIPName AZUREVMpip | Update-AzureVM

Update-AzureVM : BadRequest: Virtual machine AZUREVM cannot have both secondary network interfaces and public IPs. The
combination is not supported.
At line:1 char:92
+ ... me AZUREVMpip | Update-AzureVM
+                    ~~~~~~~~~~~~~~
    + CategoryInfo          : CloseError: (:) [Update-AzureVM], CloudException
    + FullyQualifiedErrorId : Microsoft.WindowsAzure.Commands.ServiceManagement.IaaS.UpdateAzureVMCommand

Is there something wrong with the syntax i'm running? Or is assigning a fixed PIP to a multi NIC VM not supported in Azure? Essentially id like to fix the servers IP address so that's its not lost when i 'stop' the VM.