Several reasons why this can happen on a USB device
1. corrupt file on the device
format the device or run Kill disk (remember this will wipe everything on the device).
2. the device has a write protect or hold switch
move switch to correct posititon.
3. Incorrect setting in windows Storage Device Policies
do a "regedit" for StorageDevicePolicies key.
. Get into the Registry - Press Start -> Run, enter regedit, press Ok
. Click on My Computer. Then press File -> Export, give some file name to backup the registry. Just incase you ever need to rollback.
. Navigate to HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/StorageDevicePolicies
. In the right pane select "writeprotect"
. RESET the value to '0'
Repeat the same for ControlSet001 and ControlSet002 incase they exist.
Now plug in your USB drives and it should work. Else just reboot the machine and try. This has worked on most of the machines on which I tried.