MAC authentication succeeds, port stays unauthorized (allied telesis)

Hi, I'm trying to do MAC based authentication on our switches, but for some strange reason the port doesn't want to authenticate, even though the radius server sends an Access-Accept package to the port. I did a capture on the port and the Access-Accept package is received by the port, but it port status stays unauthorized. I'm running FreeRADIUS Version 2.2.0 and the switch is an Allied Telesis AT-9000/28 Any ideas where I need to start looking? Regards Stijn