[flexcoders] Error with building dataGrids dynamically

[markgoldin_2000]

I have a VBox which holds two dataGrids:
override protected function createChildren():void
{
        super.createChildren();
        trainHourSymbol.columns = newColumns;
        trainHourSymbol.height = 50;
        addChild(trainHourSymbol);
        trainDepartGrid = new destinationGrid();
        trainDepartGrid.height = 130;
        addChild(trainDepartGrid);
        trainReceivingGrid = new destinationGrid();
        trainReceivingGrid.showHeaders = false;
        addChild(trainReceivingGrid);           
}
Then I dynamically add columns to both grids. Interesting that if I 
supress headers for either grid then I am getting this:
TypeError: Error #1010: A term is undefined and has no properties.
        at mx.controls::DataGrid/drawColumnBackground()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\controls\DataGrid.a
s:3010]
        at mx.controls::DataGrid/drawLinesAndColumnGraphics()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\controls\DataGrid.a
s:3305]
        at mx.controls::DataGrid/drawLinesAndColumnBackgrounds()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\controls\DataGrid.a
s:3205]
        at mx.controls::DataGrid/updateDisplayList()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\controls\DataGrid.a
s:1504]
        at mx.controls.listClasses::ListBase/validateDisplayList()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\controls\listClasse
s\ListBase.as:3281]
        at mx.managers::LayoutManager/validateDisplayList()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\managers\LayoutMana
ger.as:602]
        at mx.managers::LayoutManager/doPhasedInstantiation()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\managers\LayoutMana
ger.as:675]
        at Function/http://adobe.com/AS3/2006/builtin::apply()
        at mx.core::UIComponent/callLaterDispatcher2()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\core\UIComponent.as
:8460]
        at mx.core::UIComponent/callLaterDispatcher()
[E:\dev\3.0.x\frameworks\projects\framework\src\mx\core\UIComponent.as
:8403]

Can someone help, please?

Thanks