I'm getting the same 'Slot 150 is already occupied by eloraam.machine.BlockMachine@10db5b3f when adding buildcraft.factory.BlockMiningWell@31438dbe' error that Subrose reported in his follow-up post, while combining IC2 1.71, Buildcraft 2.2.12 and RedPower 2.0 PR4d). In my case, it's a client side only installation, and I've successfully combined all three mods in the past prior to 1.71.
Renaming the RP zips made no difference.
Edit: I ended up solving the problem by poking around and deleting both the buidlcraft and redpower folders in the minecraft root and all the associated .cfg (and mod_*.cfg) files with it that I could find. Running it again regenerated them and it worked eventually.