As Dalton said you have a Driver Issue and since you have already said that you have removed and reinstalled the driver there are a couple of options left.
The first one is to remove the driver shut down the computer and restart it then plug in the USB device and load the driver. You may be required to restart the system again after the driver install to get it working properly.
If that doesn't work forget about the USB drive temporally and log onto the makers Web Site or the Caddies Makers Web Site and see if there are any new drivers for the device and download them and then do the above again with the new drivers.
If none of that works you will then have to decide what you can do without as you have a software conflict between the Activesync and the drivers for the USB device. At this stage it might be worthwhile trying other USB devices in the computer to see if it really is a driver issue or that Active sync has disabled the USB ports partly.
You should also go into System Management and see if you have any Yellow circles by the USB hubs or individual connections as you may need to install some new USB drivers for the M'Board which will be available from the M'Board makers web site.
Lets know if none of that helps.
Col