In AutoCAD Civil 3D 2009 while exporting polyline to shape object in Map , you will get Fatal error. Also you will not receive the object type selection Point, Line, Polygon or Text in the Map Export dialog selections tab.
At the same time if you did it with AutoCAD Civil 3D 2008, then you will be able to do it properly.
To overcome this you need to modify Mapexport.ini
Location of mapexport.ini : C:\Documents and Settings\All Users\Application Data\Autodesk\C3D 2009
Then open mapexport.ini
Scroll down to the [SHP] section and change it to this
Note the EntTypes values.
As you modify ini file, you will get the dialog as shown below
Now you the selection dialog as well will be able to export it in to shape.