summary judgment stage in the absence of undue prejudice to the plaintiff, bad faith or dilatory motive on the part of the defendant, futility, or undue delay of the proceedings.” Saks v. Franklin Covey Co., 316 F.3d 337, 350 (2d Cir.2003). AmSouth first asserted its estoppel defense at the summary judgment stage of this litigation. At that time, the Roses had an opportunity to respond substantively to the defense. They also had the opportunity to object to AmSouth’s failure to raise estoppel formally in the pleadings. The Roses did not object. Nor do they argue on appeal that they were prejudiced by AmSouth’s procedural error. Consequently, the District Court properly considered the merits of AmSouth’s estoppel defense. See Curry v. City of Syracuse, 316 F.3d 324, 331 (2d Cir.2003) (<HOLDING>). II. The Merits of AmSouth’s Estoppel Defense
holding that a defendant avoids  causing undue prejudice by providing the plaintiff with notice and the opportunity to challenge an affirmative defense holding that laches is an affirmative defense holding that fair use is an affirmative defense holding that there was no prejudice where had the district court allowed the moving party the proper opportunity to respond the evidence would have been properly in front of the district court holding that unpleaded affirmative defense was properly considered by the district court where plaintiff had notice of the defense and an opportunity to respond