Upgraded our controller envoironment from 6.3.8 to 6.4.2.3 and am getting this error also...Only on the 6000-M3 and 3600 controllers....go figure.
Dec 18 09:41:11 :319001: <ERRS> |ARM Process| Unexpected (arm process) runtime error at dot11v_btm_req_cb, 75, Unable to find STA d4:f4:6f:75:55:6d
Dec 18 09:49:17 :319001: <ERRS> |ARM Process| Unexpected (arm process) runtime error at dot11v_btm_req_cb, 75, Unable to find STA d8:bb:2c:18:81:d4
Everything else is running ok, even our Clearpass...