As the error message explains, PHP couldn't find any class definition for "sid" so it doesn't know what you're trying to do.
Out of boredom, I downloaded the app from Sourceforge and noted this line:
include_once("$INCLUDE_PATH/engine/sid.class.php");
Now personally, I would've made that a require_once(), but shrug not my app.
Either way, make sure it's finding all of the files it needs. Turn error_reporting up to E_ALL if you haven't already.