Comment 91 for bug 548992

I've also seen this happening in my office: we have several WLAN access points with the same ESSID, and the wireless connection disconnects quite often, usually not lasting longer than one minute.
Restarting network manager while being connected to the WLAN worked for me:

initctl network-manager stop
initctl network-manager start

After this, the connection has been stable for days. But I tried this solution only once, so I'm not sure whether it works reliably or not.