45 F.3d 311, 317 (4th Cir. 2006). A district court abuses its discretion when it materially misapplies the requirements of Rule 23. See Gunnells v. Healthplan Servs., Inc., 348 F.3d 417, 424 (4th Cir. 2003); Thorn, 445 F.3d at 317-18 ("A district court per se abuses its discretion when it makes an error of law