SharePoint Developer Dashboard Error

Hello,

When i try to enable Developer Dashboard in sharepoint 2010 front end server using the below commands

$service = [Microsoft.SharePoint.Administration.SPWebService]::ContentService
$addsetting =$service.DeveloperDashboardSettings
$addsetting.DisplayLevel = [Microsoft.SharePoint.Administration.SPDeveloperDashboardLevel]::OnDemand
$addsetting.Update()

Please guide me

Thank you,

Sai