[quote=@Zarkun]
There was something about the Council too, but I don't remember what it was. It's been awhile since I watched that episode.
[/quote]

"The time has come for Erza Scarlet to fulfill the promise made to Natsu; to fight him. All the other Fairy Tail Mages are chatting a bit as the battle starts. Shortly after Erza and Natsu start to get serious, a Messenger from the Magic Council disturbs the fight. He has come to arrest Erza for the damages she made during her job in destroying Eisenwald and the Lullaby.[1]"

During the Lullaby Arc.

This, according to the wiki, is why she was arrested. Which by memory, is accurate. Because I do not think at that time Fairy Tail went against the Council. Natsu was pretty much thinking it in order to save Erza, but in the end got thrown in with her while she explained it was all a facade.

Everyone was telling him "No you can't go against them! You'll get your ass kicked!"

She was basically being taken responsible for all the destructive shit Fairy Tail tends to do. XD

Unless she was arrested again that I'm not aware of.