Error when loading PHPExcel/Worksheet

Code:
$this->load->library('PHPExcel');

$this->load->library('PHPExcel/IOFactory');



$objPHPExcel = new PHPExcel();

$objPHPExcel->getActiveSheet()->setTitle("Feuil 1");

$objPHPExcel->setActiveSheetIndex(0)

 ->setCellValueByColumnAndRow(1, 2, "I'm a test")

 ->mergeCellsByColumnAndRow(1, 2, 5, 2)

 ->getColumnDimension(5)->setAutoSize(true);



$this->load->library('PHPExcel/Worksheet');

$this->load->library('PHPExcel/Worksheet/BaseDrawing');

$this->load->library('PHPExcel/Worksheet/Drawing');



$objDrawing = new PHPExcel_Worksheet_Drawing();

$objDrawing->setName("logo");

$objDrawing->setDescription("Tt's my logo");

$objDrawing->setPath("/images/logo.png");

$objDrawing->setCoordinates('B2');

$objDrawing->setWorksheet($objPHPExcel->getActiveSheet());

$objPHPExcel->getActiveSheet()->getStyle('B2')->getAlignment()->setVertical(PHPExcel_Style_Alignment::VERTICAL_CENTER);

$objPHPExcel->getActiveSheet()->getStyle('B2')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);



// Save it as an excel 2003 file

$objWriter = IOFactory::createWriter($objPHPExcel, "Excel5");

$objWriter->save("system/docs/test.xls");