I have that same issue... WD external HD, tried to see it on 2 computers... It DOES show up in Disk Management but has no letter assigned... When I right-click on it and try to assign a letter a popup appears and says: "The operation failed to complete because
the Disk Management console view is not up-to-date. ..."
I uninstalled the driver and re-installed it, same problem...
Don't want to lose the DATA...
Cheers.