Possible Errors under InvalidOperationException

  1.  Telerik.Web.UI.RadComboBox with ID='PageSizeComboBox' was unable to find an embedded skin with the name 'Blue_Theme'. Please, make sure that the skin name is spelled correctly and that you have added a reference to the Telerik.Web.UI.Skins.dll assembly in your project. If you want to use a custom skin, set EnableEmbeddedSkins=false. at Telerik.Web.UI
  2. The connection was not closed. The connection's current state is connecting. at DataAccessLayer
  3. Only one instance of a ScriptManager can be added to the page. at System.Web.Extensions