Start Building Professional
Web Apps Today

i get an error combo2.clearAll is not a function. I have used combo2 = mygrid.getCombo(2); combo2.clearAll();

Are you using dhtmlxCombo or combo as co|coro excell type ?
In second case the syntax will be
    grid.getCombo.clear()

http://www.dhtmlx.com/docs/products/dhtmlxGrid/doc/articles/Selectbox_collections.html#grid_art_selectbox