Problems with CA using PEAP/TTLS

Dear list. I'm using freeradius 2.2.5 on debian for authentication of wireless access. The problem is that authenticating clients (I'm using PEAP/TTLS) works only if the CA-certificate is ignored by the client side. When trying to authenticate the clients using the CA in Network-Manager the authentication fails. The server certificate of freeradius is correctly signed and the public CA is selected at the clients (linux using Network-Manager). Is there a possibility to catch the server certificate on the client side after the transfer to the client. And then checking this server certificate signature against the locally installed CA-certificate by hand? For example using tcpdump? Many thanks in advance Jens