Wikimedia Bugzilla is closed!

I've changed LocalSettings.php entries as follows:
$wgFileExtensions = array( 'png', 'gif', 'jpg', 'jpeg', 'xls', 'zip', 'pdf',
'ppt', 'doc', 'csv', 'xlm', 'xlw', 'xlt' );
$wgEnableUploads                = true;

For some reason, uploads do not work for Excel (xls) files, but they do work for
another new file type, pdf.  When I try to upload an Excel file I get the error:

Upload warning
The file is corrupt or has an incorrect extension. Please check the file and
upload again.

I've tried with Mozilla 1.0.7 and IE, and reduced the file to very simple
filenames and no paths (C:\filename.xls), all to no avail.

Is there any Wiki log file or debugging that I can turn on to see what's going on?

Thanks!