Using the most stable version of Buildcarft 6.1.18, I get a crash every time having to do with java.lang.NoClassDefFoundError: buildcraft/core/triggers/BCTrigger,
heres the crash report

http://pastebin.com/d7s9dmTr

and the forge log

http://pastebin.com/5j7MmAkH

Fairly sure this is a problem with buildcraft or an incompatibility, all mods using the buildcraft api were updated. Forge veriosn is 10.13.1.1217(Running Cualdron)

I believe the problem is BuildcraftAdditions since thats where minecraft crashed, and also there is a version 1.7.2 available which says it got updated to the new BC API, and you are using version 1.6.4

that is indeed the case here, you jeed to update you BCA