[For some reason I can't reply to the BC4 thread; I'll try again.]
I had a crash, described in the BC4 thread on both of my Macs running 10.6.8. After feedback and some experimentation, it appears to be an issue with the database but since the system crashes on startup, I have no way to identify what that issue is.
What do I need to provide, if anything, to help debug this? Not being able to upgrade BC3 data to BC4 would definitely be a deal-breaker for me.