I recently fielded a support call from a frantic customer that went something like this: “Help! Nobody can post anything! All we get is a message that Item Ledger Entry is locked by another user! AAAAAAHHH!!!”
Very useful. The system knows enough to realize there is a block, but won’t bother to tell you which user is causing the problem. The usual fix is to restart the service tier, SQL service, or to reboot the whole SQL server.