I came across a major compatibility issue with Internet Explorer 7 and Microsoft Office 2007/3.

Headers sent cause IE to try to open the file inline but for the 90% of tests the content was corrupted or IE was unable to handle the file. I fixed the problem changing content disposition header to attachment

header("Content-Disposition: attachment; filename=\"" . $filename . ".xls\"");

and with 2 additional headers that force the browser to not cache the request. Here's the final piece of code

    // deliver header (as recommended in php manual)
    header("Content-Type: application/vnd.ms-excel; charset=UTF-8");
    header("Expires: 0");
    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
    header("Content-Disposition: attachment; filename=\"" . $filename .

".xls\"");

Much better. Thank you.

Thanks for this input/fix. I will try to improve the sent header in one of the next version. It's quite difficult to test this in all MS/Office/IE combinations.

Outputting to IE over SSL/HTTPS also causes and issue due to it not being able to interpret the header correctly.

I added the following additional header to your code :-

header('Pragma: public');