I got this instead of the Month on an 1.3 upgrade:
Still a problem. Calendar Month does not advance a month by clicking the right arrow.. The same on two different servers and with the 1.3 Beta and Moodle latest.
My last install was:
<?php // $Id: lib.php,v 1.27 2004/05/10 17:09:05 moodler Exp $
And the Calendar will go back in months but not forward.
I now updated again via cvs and everything works great.