I am not a Mac person, so my advice might not work.
Can you move the catalog file from via Mac Finderfrom your drobo to another folder? Best a new one that you created.Lr doesn't bother about lock-fiiles in other folders; only when a lock-file is directly besides the catalog will it prevent Lr from opening.
BTW: There were some reports on this forum about problems created with time machine backup. It is best to exclude the folder with the Lr catalog from the time machine backup and do the catalog backup with the feature built into Lr.
