I have no idea what caused it, but I used all of the latest versions of BC, BC-A, and Eureka and this is the crash I received: http://pastebin.com/qrApXY8w

download http://nallar.me/buildservice/job/Buildcraft/590/
and http://ci.tterrag.com/job/Buildcraft%20Additions/16/
delete Eureka Jar and try starting up again

new eureka and BCA version will be released soon

Thanks to both of you for your quick responses, I suspected the release itself was the problem, I'll the linked versions for both you posted above.