Ok thats fair - then I would make the following changes ...

Code:

Function ChangeVLKey($VOL_PROD_KEY)
  Dim $obj, $objects, $result
  ;Key is without hyphens (ABCDEFGHIJKLMNOPQRSTUVWXY)

  $objects = GetObject("winmgmts:{impersonationLevel=impersonate}").InstancesOf("win32_WindowsProductActivation")
  $ChangeVLKey = @error
  For Each $obj in $objects
    $result = $obj.SetProductKey($VOL_PROD_KEY)
    $ChangeVLKey = @error
  Next
EndFunction


Basically adding this line after the GetObject:

$ChangeVLKey = @error

This statement kills two birds with one stone

1) It initializes the return code to "something", which it wasn't doing before

2) It will catch a failure on the GetObject and return the code.