How to handle this Error !!!!!!!

//

 string conString = @"Data Source =.; Initial Catalog = XXXX; User Id = XXXX; Password = XXXX;";
            SqlConnection sqlCon = new SqlConnection(conString);
            sqlCon.Open();
            SqlDataAdapter da = new SqlDataAdapter("select RollNo,Color_Name,Cand_Name,BatchNo from Batch_View  where BatchNo='" + BatchNo + "'", sqlCon);
            System.Data.DataTable dtMainSQLData = new System.Data.DataTable();
            da.Fill(dtMainSQLData);
            DataColumnCollection dcCollection = dtMainSQLData.Columns;  


 Export Data into EXCEL Sheet

      Microsoft.Office.Interop.Excel.ApplicationClass ExcelApp = new Microsoft.Office.Interop.Excel.ApplicationClass();   // this is where the problem is 
            ExcelApp.Application.Workbooks.Add(Type.Missing);
            // ExcelApp.Cells.CopyFromRecordset(objRS);
            for (int i = 1; i < dtMainSQLData.Rows.Count + 1; i++)
            {
                for (int j = 1; j < dtMainSQLData.Columns.Count + 1; j++)
                {
                    if (i == 1)
                    {
                        ExcelApp.Cells[i, j] = dcCollection[j - 1].ToString();
                    }
                    else
                    {
                        ExcelApp.Cells[i, j] = dtMainSQLData.Rows[i - 1][j - 1].ToString();
                    }
                }
            }

            ExcelApp.ActiveWorkbook.SaveCopyAs("C:\\Documents and Settings\\All Users\\Desktop\\test.xls");
            ExcelApp.ActiveWorkbook.Saved = true;
            ExcelApp.Quit();
            MessageBox.Show("Data Exported Successfully into Excel File");