The previous update to Base had a bug which caused a crash on launch for users running Mac OS 10.7. It did not affect users on 10.8 or newer.
Version 2.4.1 of Base fixes this bug and is available immediately for download from this site. People who have purchased Base via the Mac App Store will have to wait a little longer as the update must be approved by Apple. I have requested an expedited review, so hopefully this will not take long.
I apologize for the trouble this has caused all those affected, and encourage anyone with questions to get in touch.