Canjacob, it's not clear from your request what you are doing. AllowSizing is a property of the iGrid column object (iGCol) but not of the whole grid. Maybe, you meant the AutoResizeCols property? It enables a special mode when iGrid automatically adjusts the width of all the columns to place all of them in its visible part so we do not need the horizontal scroll bar. If the H scroll bar is present in this case, it may happen if you set its visibility to 'always'.
Looking at all this, we definitely need a sample project we can launch to reproduce the issue. Can you prepare and send us one?