On a Windows Server 2012R2 machine, I use StorageCraft Shadowprotect to back up the server nightly. We have 5 USB hard drives, one for each day of the week. The backup job runs nightly and the office manager disconnects the drive in the morning and plugs in the next USB drive. It seems to work fine for a several days and then all of a sudden the drive will no longer appear until you move it to a different USB port. It will work again for a few days and then not be visible as an attached drive once again. I just don't get it. We need to cycle through drives but it seems like Windows doesn't like us doing that. Is this a known problem with Windows Server 2012R2?