I have a Cisco 4400 series controller with 15 LWAPs configured.

I've noticed that some Windows CE wireless clients (proprietary hand helds) generate around 1200-1500

Data Retries per 500-900k bytes sent.

Doesn't happen to all of them, but it seems to be specific to 2-3 APs.

What could cause the Data Retries?

Interference seems to be pretty low in the area, and I haven't gotten any alarms on the controller, but I have users complaining to "waiting for data" when using the handhelds.