I tried loading a lot of different html files but even those generated trough PHPExcel's own writer returned the same error. I've confirmed the file is there and readable and will post the load code as well as the file below:
the php code i'm using:
$objReader = new PHPExcel_Reader_HTML();
$objPHPExcel = @$objReader->load($file_path.'fisier_test.html');
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment;filename="ExportProduseOportunitati.xls"');
header('Cache-Control: max-age=0');
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel5');
$objWriter->save('php://output');
And I've pasted the HTML in this jsfiddle here. It won't look right because I kept the html and head tags and the css is included in the head, but I wanted to keep the html file intact so I'll leave it like that. (the file was created with PHPExcel)
I'm just trying to see if I can make PHPExcel work for converting HTML into XLS.
This issue has been raised and fixed in the develop branch on github.