Wireless connection re-authentication

I have a Cisco 1100 wap that is working well but every now and then my connection on my ThinkPad drops and the wireless icon in my system tray show that wireless is attempting to re-authenticate with the IAS radius server. Eventually is re-connectesd. Curious if anyone has seen this and has some ideas ?
Client computer runs XPP and we have IAS running on Windows 2003 std server (its a DC too)