AFAIK GridCtrl can Xmlize itself but cannot Xmlize editable fields. In fact if you try to Xmlize the editable fields you just save their values, but in any way an editable field represent a GridCtrl column.
In summary, you would have to Xmlize all GridCtrl. To store just a column you would have to extract it by hand and store it like for example a Vector<Value>, and load it and write it over a GridCtrl.
In addition please remember that when you Xmlize a Gridctrl, before load it you have to add all columns (AddColumn()) before.