Horayot 2 - Court Makes a Mistake
If the court ruled to transgress one of the commandments written in the Torah - for example, they decided that a certain type of blood is allowed to be eaten, and an individual did it, relying on their words - he is free from liability. Whether he ate the blood together with them at a meal, or after observing them, or even if they just ruled it permitted, but did not do it themselves, since he relied on their words, it is not his fault.
However, if he was one of the Sages of the court, or even one of the students who was worthy to be on the court, and he knew that they erred, but he nevertheless followed their ruling, he is liable to bring a sin offering. If he knew that they erred, then why did he do it? Because he mistakenly thought that the mitzvah to follow the words of the Sages applies even in this case.
Art: Thomas Satterwhite Noble - The Price of Blood