$ diskutil list # To list all your connected HDD
$ sudo fsck_hfs -rf /dev/disk2s99 # To repair your disk2s99,
# this might take a while.
# **USE AS YOUR OWN RISK.**
** /dev/rdisk2s2
Executing fsck_hfs (version hfs-285).
** Checking Journaled HFS Plus volume.
The volume name is Time Machine at Work
** Checking extents overflow file.
** Checking catalog file.
** Rebuilding catalog B-tree.
** Rechecking volume.
** Checking Journaled HFS Plus volume.
...Note: If you encounter Resource busy error, try killing your current Disk Utility’s fsck_hfs process from Activity Monitor or your Terminal - 60% of the time, it works every time.
Update: When this also failed, you probably want to try out DiskWarrior. It actually worked for me:
