I think beans are ok, and protein (like meat) is avoided because it's stinky. I doubt it would make your worms sick, esp. if fed only in moderation :)

Protein poisoning usually occurs when you consistently feed too much protein to the worms. I vaguely recall that nitrogen is the worst for them, but I may be off on that. It happens over several feedings of the same stuff. Often people will experience this with a bin that is just for raising worms and not for composting. They feed ground up oats and corn (which has lots of nitrogen) alone and the worms end up with problems. I've caused the problem once that way when experimenting with a breeding bin. It took weeks of feeding the same thing over and over. For the most part, variety and good pH will prevent the problem. Your beans will be fine.