Top visitor report error

I click on the top visitor reports link and get this error.

user warning: Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8_unicode_ci,IMPLICIT) for operation 'like' query: SELECT COUNT(a.uid) AS hits, a.uid, u.name, a.hostname, SUM(a.timer) AS total, ac.aid FROM accesslog a LEFT JOIN access ac ON ac.type = 'host' AND LOWER(a.hostname) LIKE (ac.mask) LEFT JOIN users u ON a.uid = u.uid GROUP BY a.hostname, a.uid, u.name, ac.aid ORDER BY hits DESC LIMIT 0, 30 in /access/public_html/XYZ/modules/statistics/statistics.admin.inc on line 87.