With MC 1.6.4, Forge 9.11.1.935, and the following 6 mods, Minecraft crashes. (Minecraft still crashes if the Mekanism Tools and Generators aren't installed. So 4 mods are needed to reproduce the error.)

DartCraft Beta 0.2.10.jar
industrialcraft-2_2.0.278-experimental.jar
MekanismGenerators-v5.5.7.254.jar
MekanismTools-v5.5.7.254.jar
Mekanism-v5.5.7.254.jar
Railcraft_1.6.2-8.1.0.0.jar

Crash Log:
http://pastebin.com/anSwmv6v
Full Forge log:
http://pastebin.com/ie2xSePM

Removing any single mod allows Minecraft to load.

I also posted this to Mekanism's issue tracker:
mekanism/Mekanism#313
and to DartCraft's MC forum thread:
http://www.minecraftforum.net/topic/1686840-164-dartcraft-beta-0210/page__st__940#entry25228524

Looks like IC2 API issues caused by Mekanism.

I was able to fix this by changing both of the config options to false in Railcraft's IC2 section for refined iron.

It was some weird interaction between the 4 mods regarding refined iron. If any single mod was uninstalled, the crash wouldn't occur.