Html.RenderPartial("Main_Menu");
You're not giving the partial view a model so (I think) it uses the model of the parent which is your Tuple, however Main_Menu needs vw_100_QUERY_FOR_XLS_WEEK_IN_PROGRESS_016_Forecast_Follow_Current_Data. Try something like
Html.RenderPartial("Main_Menu", Model.Item2);
that will pass the ...._Current_Data part of the parent model to the partial view as its own model.