Crot was not working on our website http://moodle.coep.org.in

I checked the apache2 error log in /var/www/apache2/error.log and found the following line:
[Mon Sep 24 09:32:03 2012] [error] [client 10.1.101.150] PHP Warning: Division by zero in /var/www/moodle/plagiarism/crot/lib.php on line 70, referer: http://moodle.coep.org.in/moodle/course/view.php?id=134

The same line is repeated for many other courses also.

The line of code in lib.php, in question, is this:
$perc = round(($similarity->max / $numbertotal->cnt) * 100, 2);