You have a mistake in your code. I guess there is a GridControl control on the page with ID 'GridControl1' and you are creating the instance of its 'ID" with this code-And that too, two times in the same scope...
GridControl1 Gd = new GridControl1();
range = worksheet.UsedRange;
GridControl1 Gd = new GridControl1();
Rather you should create a instance of Gridview control like this -
GridControl Gd = new GridControl();
range = worksheet.UsedRange;