Updater has stopped after downgrading to B137 from B143

So I was trying to test the beta Lollipop on my MT7-L09 and I used the Update OTA to install B137, so that I can install B308 and B317, respectively.
Now everytime I try to open Updater, it crashes with the toast: Updater has stopped.
Has anyone encountered it / how did you fix this issue? Google didn't seem to be very helpful on this topic.