Error :The DetailsView "dv" fired event ModeChanging which wasn"t handled.

I can't get the Detailview in GridView to change to EditMode i keep getting
error :
:The DetailsView 'dv' fired event ModeChanging which wasn't handled.

In the ModeChanging event below i looked for the Detailview and added the
changeMode but still doesn't work

protected void dv_ModeChanging(object sender, DetailsViewModeEventArgs e)

{

if (e.NewMode == DetailsViewMode.Edit)

{

DetailsView gv = new DetailsView();

gv = (DetailsView)this.GridView1.FindControl("dv");

gv.ChangeMode(DetailsViewMode.Edit);

}

}

I have a DetailView dv in a GridView GridView1 template like so :