Plugin generates a link to download xml as

/blocks/configurable_reports/viewreport.php?id=29&courseid=128&download=1&format=xls

and not as:

/blocks/configurable_reports/viewreport.php?id=29&courseid=128&download=1&format=xls

which may cause a problem on some servers. (empty xml)

Problem is generated by the s() function, if it is not there the url is correct

$wwwpath .= "&$key=" . s($val); 

// TODO Use moodle_url.

$output .= '<a href="' . s($wwwpath) . '&amp;download=1&amp;format=' . s($e) . '">