Thread:Extension talk:LiquidThreads/"WatchAction" error

I am getting the following error after trying to go from the 1.17 version to the trunk version (LiquidThreads-trunk-r96248.tar.gz):

2011-09-04 20:10:51: (mod_fastcgi.c.2711) FastCGI-stderr: PHP Fatal error: Class 'WatchAction' not found in /wiki/extensions/LiquidThreads/classes/Thread.php on line 115

I am using lighttpd with fastcgi and php 5.3.2. My mediawiki version is 1.17.0.