Filter by parent in admin (doesn't work)

Hello,

This post is in regards to: Filter by Parent in Admin (Plugin, Version 1.2, By James Irving-Swift)

I downloaded this plugin, but it stopped working out of the blue…

Here’s my site address: http://www.xenosource.net

Also, here’s a screenshot of my dashboard where a field should appear to filter through pages: http://www.xenosource.net/wp-content/uploads/2012/04/Problem.bmp

Someone please help me fix this. Thanks!