I try to select line segments from a layer "t_Pavement_Line which is open in TOC using the following line:
    arcpy.SelectLayerByAttribute_management("t_Pavement_Line", "NEW_SELECTION", '"ROAD_CLASS" = \'%s\'' % classname)
I get this Error message:
    ExecuteError: ERROR 000622: Failed to execute (Select Layer By Attribute). Parameters are not valid.
ERROR 000628: Cannot set input into parameter in_layer_or_view.