I have recently had this problem with my Cn 32GB memory device on Windows XP.
Thank to this and other forums I managed to reformat it as below:-
1. Open a DOS command window: Start>run and type cmd then click 'OK'
2. Type: format <drive>: where <drive> is the drive letter assigned to the memory stick shown in Windows Explorer.
3. At message: "Insert new disk ....." press 'Enter' key.
4. At message "Format cannot run because volume is in use ........ would you like to force a dismount on this volume? <Y/N>" press the 'Y' key.
USB devise will then be reformatted and usable in Windows XP.
NOTE: ALL DATA ON THE USB DEVICE WILL BE DELETED.
Hope this helps others.
John Bicknell
Lancashire, England