How do I get an error reason from InstallProductKey (SoftwareLicensingService) in PowerShell?

I'm using some PowerShell functions to configure Windows product keys and activation. I get an instance of the SoftwareLicensingService and call InstallProductKey, like this. The trap block with super formatting is extra to help debugging.

trap [Exception]
{
    "=================================================="
    "Trapped:   $($Error[0])"
    "=================================================="
    "Exception: $($_.Exception)"
    "--------------------------------------------------"
    ""
    break
}

$service = Get-WmiObject -Query "SELECT * FROM SoftwareLicensingService"
$service.InstallProductKey("12345-12345-12345-12345-12345")
$service.RefreshLicenseStatus() | Out-Null

The error condition is an invalid product key. I know this because I entered it manually into the Activate Windows dialog from the System panel. But, the script only ever shows me the WMIMethodException or the COMException.

==================================================
Trapped:   Exception calling "InstallProductKey" : ""
==================================================
Exception: System.Runtime.InteropServices.COMException (0xC004F025)
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
   at System.Management.ManagementObject.InvokeMethod(String methodName, ManagementBaseObject inParameters, InvokeMethodOptions options)
   at System.Management.Automation.ManagementObjectAdapter.InvokeManagementMethod(ManagementObject obj, String methodName, ManagementBaseObject inParams)
--------------------------------------------------

Exception calling "InstallProductKey" : ""
At line:14 char:31
+ $service.InstallProductKey <<<< ("12345-12345-12345-12345-12345")
    + CategoryInfo          : NotSpecified: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : WMIMethodException

I don't get a return code from the method (despite the documentation stating I do, can't find a list of error codes anyway). Do you know how to get the activation (or product key install) error reason?

As far as I can see there's no message there. Adding these to your trap:

$_ | fl * -Force
$_.Exception | fl * -Force

Returns everything that is there in the exception and there is nothing useful. So I googled a bit and found a piece of C# code here: http://www.dozty.com/?tag=change-windows-7-product-key-c-sharp They were cathcing ManagementException and in C# it seemed to work a bit better. I have rewritten that code into PowerShell and was trying to catch ManagementException, but without luck:

trap [Exception]
{
[System.Management.ManagementException] $_
break
}
$classInstance = new-object System.Management.ManagementObject("root\CIMV2","SoftwareLicensingService.Version=`"6.1.7600.16385`"", $null);
$inParams = $classInstance.GetMethodParameters("InstallProductKey")
$inParams["ProductKey"] =  "12345-12345-12345-12345-12345"
$classInstance.InvokeMethod("InstallProductKey", $inParams, $null)

It throws: Cannot convert the "System.Runtime.InteropServices.COMException (0xC004F050)"