We've got a single school with 45 Cisco Access Points (Aironet 1142N). All Windows 7 ENT 32bit laptops. Lenovos and Dell Lattiudes.
We're seeing students leave the school for the day, come back in next day and for some of them, the wireless cards are just disabled. We enable them and they're fine.
This happens every day....both Lenovo L420 and Dell Lattitude E5410
I can't nail down why this is happening.