The gemara concludes that in general there is no shlichus for an aveira, meaning that the agent is responsible for his own actions and they cannot be blamed on the sender. Tosafos holds that this only applies so long as the shliach is doing it intentionally and realizes that it is an act of aveira, but if the shliach doesn't realize that it is an aveira (he does it b'shogeg) then shlichus does apply and the sender is responsible. The Ketzos Hachoshen (348:4) discusses this and proves from rashi 50a who says that by me'ila if the sender is intentional and the agent is shogeg, then since the sender can't be in violation of me'ila (since me'ila is only b'shogeg), the regular rule of "ein shliach l'dvar aveira" kicks in to make the agent liable. From the fact that Rashi applies "ein shliach l'dvar aveira" to even a case where the shliach is shogeg, implies that he argues on Tosafos. The ketzos continues that Tosafos who holds that the shliach should not be liable when he is shogeg, would have to explain the gemara that the shliach violates me'ila based on rashi in chagiga 10 who says that since the ba'al habayis remembers that the money is hekdesh, he is mevatel the shlichus so that the agent is no longer his shliach and therefore liable for his own actions.
The Pischei Teshuva (Even Ha'ezer 119:6) quotes the Nodeh B'yehuda (kama 75) who is mechadesh based on tosafos in baba metziah, that ein shliach l'dvar aveira doesn't merely make the agent responsible for the aveira, but it also invalidates the act that was done. Therefore, if one sends an agent to divorce his wife against her will (thereby violating the cherem), the divorce is not binding. The Pischei Teshuva says that many achronim took issue with this ruling, but the Nodeh B'yehuda justified his position in subsequent teshuvos. It is slightly meduyak in rashi 42b who says that eish shliach l'dvar aveira is only in respect to being mechayev the sender, implying that for all other purposes the shlichus is binding. I think i once mentioned on this blog previously that his mechutan referred to a mishna l'melech who conforms to this ruling that the action is invalidated. The Nodeh B'yehuda responded by saying that the reference to the mishne l'melech was just trying to undermine his own chiddush, because there is no mishne l'melech regarding this, it is "my own chiddush". The Pischei Teshuva continues to show how this opinon is actually apparent from the mishneh l'melech in hilchos geneiva (3).
Based on the opinon of Tosafos who says that if the shliach is shogeg then yesh shliach l'dvar aveira, it will come out that in the case of the nodeh b'yehuda, if the agent was unaware of the cherem that forbids divorcing a wife against her will, we would say "yeish shliach l'dvar aveira" so that the divorce would be binding even according to the noda b'yehuda, and that the aveira would be attributed to the husband.