After we moved to Vsphere 5.1 the "remove datastore" function in VSC throws the attached error when trying to unmount/remove a datastore from inventory. I plan on adding to the communities but I also want to see if you were aware. The datastore does get removed on the second attempt, however I think this is related to a simliar issue I get when I need to reboot a filer while the ESX server is on. After reboot, a random number of VMs show up as "inaccessible". The fix is to drill into the datastore and re-add the vm to inventory. Seems like the datastore removal is not being handled or quiesced by Vsphere properly.