This is because of a collision in the assignment of drive letters for network drives and USB drives. You must move one of the devices to a different drive letter to access.
MS Setup Windows so that the subsystem that manages local disk access cannot see into the subsystem that manages network disk access. This means that you have two independent subsystems assigning drive letters. Microsoft’s answer to this issue (USB and Network drive letter auto asssignments colliding) is that you should assign network drive letters starting with “Z:” and work backwards.
If you are looking for an automated solution, the best I have seen is:
USB Drive Letter Manager
First, you have to make sure that the computer system where you are trying to plug the storage device is not infected with any malware program. Remember that viruses or malware programs have the ability to hide and delete anything in your computer system. Another thing is make sure that there is no software (third party software) which is designed to restrict the use of storage devices to the computer system.