Hi... I am using Inventor API using vb.net coding.and my need is to Change the material of the document.my code is working but when I change the material the mass didn't changed.anyone know what is the problem.here is my code.            Dim oParameters As Parameters            oParameters = oPartDoc.ComponentDefinition.Parameters()             Dim oLengthParam As Parameter            oLengthParam = oParameters.Item _                                      ("d0")            oLengthParam.Expression = TextBox1.Text            Dim oPropSet As PropertySet            oPropSet = oPartDoc.PropertySets("Design Tracking Properties")            oPropSet.Item("Material").Value = "Glass"            oPartDoc.Update()