The most well known problem plant for bees is Rhododendron but there are quite a few others. The top ten were recently listed in a Countryfile article:
But that does raise the interesting question of why are any plants toxic to bees? BuzzAboutBees outlines the various theories with and discusses the Pollinator Fidelity Hypothesis,
Nectar Robbery Hypothesis and Drunken Pollinator Hypothesis here: Plants Toxic for Bees
Of course its not just the bees that can have problems. Honey produced from toxic nectar can also be quite dangerous for humans to consume. In fact there is a history of ‘mad honey’ being used in warfare.
The following articles from AdventuresInBeeLand and Modern Farmer cover the topic quite well and well worth a read.
I also stumbled across this fascinating documentary about the traditional gathering of intoxicating honey from cliffs in Nepal. It’s a lovely depiction of the importance of tradition and skill saving. A fascinating study of community working with nature.