DHCP Client fails getting IP Address

Hello All,
I have a WinCE 4.1 device that is using a Cisco 350 Series Client
Adapter. It is configured to get an IP via DHCP. Whenever I start
the device up within range of the AP it gets an IP with no problems.
However, if I take the device out of range (losing the IP and kicking
in the APIPA) and then 8-12 hours later bring the device within range
of the AP about 20-30% of the time it will not talk with the DHCP
server and thus get an IP from the wireless network. I have read that
many others have a similar problem. What is the resolution (i.e.
Registry change)? We have 1,000 devices that do this on a daily basis
and having 200 of them not connect to the network is a problem.
Static IP is not an option. I would like to know the root cause and
the fix. Thanks!

Any ideas? Help!