you need to update your calendar addon!

[jdleung]

if you're using the version 1.1.0 or later, you'll find a bug when it's after September.

1.go to the last image of your site
yoursite/index.php

2.click to view the previous image, the calendar disappears.

here is a updated version.
http://forum.pixelpost.org/showthread.php?t=4256