Error message when downloading View report

Thanks. I found the following error message. Does it give you any clue as how we can fix it?

PHP Fatal error: Call to a member function getGenreId() on null in F:\journals.lincoln.ac.nz\wwwroot\plugins\generic\usageStats\UsageStatsLoader.inc.php on line 78

and line 78 is below (highlighted in bold)

// is the file article full text
$genreDao = DAORegistry::getDAO(‘GenreDAO’);
$genre = $genreDao->getById($articleFile->getGenreId());
if ($genre->getCategory() != 1 || $genre->getSupplementary() || $genre->getDependent()) {
$assocTypeToReturn = ASSOC_TYPE_SUBMISSION_FILE_COUNTER_OTHER;
} else {
$assocTypeToReturn = $assocType;
}
break;

Regards,
Yanan