The Blue Cross Blue Shield plans in Minnesota, New York, New Jersey and Arizona hired Crowell & Moring LLP to represent them in a lawsuit that accuses Walgreen Co. of overcharging for prescription drugs. Before switching sides, Crowell had allegedly provided advice to Walgreen about the disputed pricing program. Rather than moving to disqualify Crowell, though, Walgreen pursued a counterclaim that contends the plaintiffs are aiding and abetting the law firm’s alleged breach of fiduciary duty.The plaintiffs challenged …