Hi,
Its seems the lun is not mounted by esx host. You can use the following options:
Use the rescan in GUI and chose both options.
If the lun does not mount using rescan look at the /var/log/vmkernel.log to diagnose the issue. Alternatively you may also try adding the storage back with existing signature if you have not created any lun clones for this lun on storage.
-f10