freeradius 2.1.8, eap-tls with 3Com AccessPoint

Hi, I've installed freeradius 2.1.8, eap-tls with 3Com Access point (3CRWE454G72). It's work fine. Unfortunately, window xp client have been disconnected/reconnected many time per day. and sometime, during it's trying to connect, I will see windows popup request the certificate as well. anyway, i just choose the right certificate, it gonna work normally. Do you have any idea ? Thank you, maxx