Got this crash when I placed a pump: https://gist.github.com/rvandenberge/977d37fef36c08da5268

When reloading the world, the client crashes again.
This is on Buildcraft 4.2.2.

1. Try upgrading to BC 5.

Do not open an issue if you're not planning to fix it, instead open a thread on http://mod-buildcraft.com/forums/index.php?board=2.0

(Also, Spacetoad, there's a small typo in the README-it's instead, not intead :P)

Don't update the BC 5, that would only make things worse. BC 5 is for MC 1.7.

But you do need to check your other mods for incompatible versions of the BuildCraft API.

^Should have clarified that it was for 1.7, sorry.

This is not another mod causing this, I can only see Buildcraft classes in the stacktrace.

A lot of mods comes with a little bit of BuildCraft in them. The BuildCraft Api that helps the mod integrate with BuildCraft. The mod can for example start using the power or add their own Gate options. You are now getting an error because one of the mods contain a piece of BuildCraft that is incompatible with BuildCraft 4.2.2.

If you removed all mods except BuildCraft I'm sure the error would go away. You can test that first and then add more and more mods until you find the one causing the problem.