Deleting a Snapshot with Powershell

I have been writing scripts to automatically take snapshots everynight.  Those work fine but I also need the ability to delete snapshots via powershell and that is where my problem is.  Here is my deletion script:

# Prompt for the Hyper-V Server to use
$HyperVServer = 'Hyperv Machine'
# Prompt for the virtual machine to use
$VMName = '01-vm'
# Prompt for the name of the snapshot to delete
$SnapshotName = 'DailyBackup'
# Get the management service
$VMMS = gwmi -namespace root\virtualization Msvm_VirtualSystemManagementService -computername $HyperVServer
# Get the virtual machine object
$VM = gwmi MSVM_ComputerSystem -filter "ElementName='$VMName'" -namespace "root\virtualization" -computername $HyperVServer
# Find the snapshot that we want to delete
$Snapshot = gwmi -Namespace root\virtualization -Query "Associators Of {$VM} Where AssocClass=Msvm_ElementSettingData ResultClass=Msvm_VirtualSystemSettingData" | where {$_.ElementName -eq $SnapshotName} | select -first 1
# Delete the snapshot
$result = $VMMS.RemoveVirtualSystemSnapshot($Snapshot)

I got this script from here : http://blogs.msdn.com/b/virtual_pc_guy/archive/2011/10/20/deleting-a-snapshot-via-powershell-hyper-v.aspx

My problem is when I hit the line 

$Snapshot = gwmi -Namespace root\virtualization -Query "Associators Of {$VM} Where AssocClass=Msvm_ElementSettingData ResultClass=Msvm_VirtualSystemSettingData" | where {$_.ElementName -eq $SnapshotName} | select -first 1

I get the error gwmi: not supported

All help is greatly appreciated!!