Man, been a while but i forgot how much i hate FreeBSD. Reminds me of the old days where solaris refused to ship their OS with a compiler or a decent shell, or require you to update /etc/nsswitch.conf to use DNS. Oh wait they still they do that with Solaris 10.. Ok, sorry tangent.
So if you need to compile mod_rails (aka passenger) on FreeBSD 7 with apache 2 and you used the default port install then you need to recompile with
make USE_THREADS=yes
and you will avoid that very nasty "Bus Error (core dumped)"
The other option is to use the Worker MPM and you should be good as well. I still cant mod_proxy to work but thats another issues.
Fun times.
