PHPExcel導(dǎo)出設(shè)置sheet的title出現(xiàn)錯誤

錯誤信息如下：

Fatal error: Uncaught exception 'PHPExcel_Exception' with message 'Invalid character found in sheet title' in E:\Project\php\cdsy_dev\lib\PHPExcel\Classes\PHPExcel\Worksheet.php:467 Stack trace: #0 E:\Project\php\cdsy_dev\lib\PHPExcel\Classes\PHPExcel\Worksheet.php(841): PHPExcel_Worksheet::_checkSheetTitle('[??????]??????-...') #1 E:\Project\php\cdsy_dev\lib\class\ExcelPortOfYearPlan.php(139): PHPExcel_Worksheet->setTitle('[??????]??????-...') #2 E:\Project\php\cdsy_dev\lib\class\ExcelPortOfYearPlan.php(209): ExcelPortOfYearPlan->getDetail(15, '[??????]??????-...') #3 E:\Project\php\cdsy_dev\lib\class\ExcelPortOfYearPlan.php(196): ExcelPortOfYearPlan->saveLink(Array, 2, Object(PHPExcel_Worksheet), true, '[??????]??????-...') #4 E:\Project\php\cdsy_dev\lib\class\ExcelPortOfYearPlan.php(188): ExcelPortOfYearPlan->saveNature(Object(stdClass), 'C', 2, 1, Object(PHPExcel_Worksheet), true, '[??????]??????-...') #5 E:\Project\php\cdsy_dev\lib\class\ExcelPortOfYearPlan.php(123): ExcelPortOfYearPlan->saveNature(Object(stdClass), in E:\Project\php\cdsy_dev\lib\PHPExcel\Classes\PHPExcel\Worksheet.php on line 467

我只要在現(xiàn)基礎(chǔ)的title上多加一個字符就會出現(xiàn)此異常，例如：
$sheet->setTitle($link_title.'a');

求解答這是什么原因?qū)е碌模?/p>