You need to bind you gridview again at rowedit
event same for rowcanel
event too your code will something look like this
protected void grd_usuarios_RowEditing(object sender, GridViewEditEventArgs e)
{
grd_usuarios.EditIndex = e.NewEditIndex;
bindGridview();
}
public void bindGridview()
{
grd_usuarios.DataSource = yourDataTable;
grd_usuarios.DataBind();
}