Azure Network Security Group - The virtual network name is not valid

Hello,

I am attempting to use the Set-AzureNetworkSecurityGrouptoSubnet  cmdlet however am receiving the following error:

Set-AzureNetworkSecurityGroupToSubnet : BadRequest: The virtual network name 10.11.x.x is not valid.

I have tried explicitly defining the VNET name and using a $vnetname variable, neither of which have worked. I can however, run Get-AzureVNetSite -VNetName 10.11.x.x and I receive a valid response, so the VNET name appears to be perfectly valid.

From what I've read, the VNET name cannot be modified and it appears to me that the only place in which the virtual network name is not valid is when using this cmdlet.

Can anybody help?