ZURICH, Oct 30 (Reuters) - Swiss plastics maker Sarna on Wednesday warned 2002 profit would be flat, scrapping an earlier forecast for a rise by at least 30 percent, due to unexpectedly high start-up costs. The firm cited start-up costs for new products and platforms at its German Paulmann & Crone car parts supplier as well as extraordinary restructuring costs as reasons for the profit warning which replaced forecasts made in August.