I have reported this on the IC2 tracker too, but I believe there is something going wrong with IC2 and BuildCraft talking to each other. When I have BuildCraft install the glass fibre cables do not connect to a Nuclear Reactor and when I place a Chamber onto the Reactor it get this crash.

Report: https://gist.github.com/artdude543/0ad490d88b50c9cc60bc

I can not work out why this crash is happening as for some it's not happening with them and some it does. If anyone could help that would be grand

But I'm guessing this an IC2 issue so it did report it there first.

Definitely Ic2. Appears to have tried creating a fluid stack with a null fluid.

As a side note, if you disable the steam mode in IC2 config you might find it works.
The reactors output either EU or Steam, the reason the cable doesn't connect is because it's expecting some form of liquid transport pipe. Change the config, you might have some luck.

Yeah I found that and it's fine now. Just have to wait for IC2 to fix there fluid issues