Be careful when you change the drive letter. If another program makes references to the existing drive letter, changing the drive letter destroys the existing references.
If an error message appears when you attempt to change a drive letter, it may be because another program is using it. If this happens, close the program that is using the device.
If you want to change the drive letter for a device, the drop-down list contains only those letters that have not been assigned to a device.