Yeah the latest FB app update broke it for me too. We'll just to wait and see if the tweak gets updated again. It may be that FB has finally removed the legacy messenger component from the app though. If that is the case, then the tweak is broken for good.
Bad news: FB removed the code.
From today (talk about the messenger code is in the comments, along with a link to another thread on the subject)): http://www.reddit.com/r/jailbreak/comments/2z6g66/facebook_messenger/
You can revert back to the previous version. Download it from Appcake, and it works.
I download the fb app v25.0
where to download v25.0
now it's v27 on app store
you would need to find the ipa for v25 somewhere else online
You can do that for free by just renaming (use iFile or Filza) the iTunesMetadata.plist file inside the app folder.
Did you do a google search?
facebook v25 ipa
Its not that hard....