In case, when you are facing colspan problem in datagarid paging section, then use this code to correcting colspan problem.

protected void dGrid_PreRender(object sender, EventArgs e)
        {
            try
            {
                DataGrid dgSidDetails = (DataGrid)sender;
                //Fix for numbering being in a left aligned column
                //For some reason, the ColumnSpan property is ignored andnot rendered
                    //unless set using the Attributes
                    if (dgSidDetails.AllowPaging == true && dgSidDetails.AutoGenerateColumns ==    false)
                    {
                        //Get the Table
                        System.Web.UI.WebControls.Table tab =
                            (System.Web.UI.WebControls.Table)dgSidDetails.Controls[0];
                        //Change the Top Pager
                        if (dgSidDetails.PagerStyle.Position == PagerPosition.Bottom ||
                            dgSidDetails.PagerStyle.Position == PagerPosition.TopAndBottom)
                        {
                            tab.Rows[tab.Rows.Count -
                                1].Cells[0].Attributes.Add("colspan",
                                tab.Rows[1].Cells.Count.ToString());
                        }
                        //Change the Bottom Pager
                        if (dgSidDetails.PagerStyle.Position == PagerPosition.Top ||
                            dgSidDetails.PagerStyle.Position == PagerPosition.TopAndBottom)
                        {
                            tab.Rows[0].Cells[0].Attributes.Add("colspan",
                                tab.Rows[1].Cells.Count.ToString());
                        }
                    }
            }
            catch (Exception ex)
            {

            }
        }