AutoCAD .NET :: How To Add Partial CUI File Tab To Current Workspace

I'm having difficulty accessing the Customization Section for a particular Partial CUI which I need to return the Ribbon Tab Source using AutoCAD 2012.

Here's the snippet

var cuiMain = (string)Application.GetSystemVariable("MENUNAME");
var csMain = new CustomizationSection(cuiMain);
//*** This line return null even when the PartialCUI exists? ****
CustomizationSection csPar = csMain.getPartialCUI("myPartialCui");
[code].......