Error in code

object does not contain a definition for 'CommandArgument' and no extension method 'CommandArgument' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)

public void PagerButtonClick(object sender, CommandEventArgs e)
    //public void PagerButtonClick(object sender, EventArgs e)
    {
        string arg = sender.CommandArgument.ToString();
        //string arg = sender.ToString();
        switch (arg)
        {
            case "next":
                //The next Button was Clicked
                if ((dgcategory.CurrentPageIndex < (dgcategory.PageCount - 1)))
                {
                    dgcategory.CurrentPageIndex += 1;
                }
                break;
            case "prev":
                //The prev button was clicked
                if ((dgcategory.CurrentPageIndex > 0))
                {
                    dgcategory.CurrentPageIndex -= 1;
                }
                break;
            case "last":
                //The Last Page button was clicked
                dgcategory.CurrentPageIndex = (dgcategory.PageCount - 1);
                break;
            default:
                //The First Page button was clicked
                dgcategory.CurrentPageIndex =Convert.ToInt32(arg);
                break;
        }
        //selpagecombo()
        //Now, bind the data!
        BindCategory();
    }