Almost certainly this is a timeout or a memory issue. The only PHPExcel limit for worksheets size is 65,536 rows and 256 (IV) columns (when using the Excel5 Writer); or 1,048,576 rows and 16,384 (XFD) columns (when using the Excel2007 Writer).
Ensure that your error logging is always enabled... use try/catch blocks to trap for any PHPExcel Exceptions. And read the PHPExcel site discussion threads on memory and performance.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…