Alvarion BreezeSecure – Cisco Problem

Hi all,
we have a problem with a Alvarion wirelees link.
Link devices are attached as follows:

– Node 1: LAN -> Cisco Catalyst 2940 -> BreezeSecure -> Antenna.
– Node 2: LAN -> Cisco Catalyst 2940 -> BreezeSecure -> Antenna.
On node2 we experiment a communication failure after 4 mt and 30 sec more or less.
If we substitute Cisco Catalyst on node 2 with a non-managed switch, the system works properly. Any suggestion?