I was having problems reading all files on an extra hard drive so I attempted to "fix" this with these commands as root:
chown dave:dave /media/250GB
chmod 644 * /media/250GB
I'm now unable to see the drive and mount it in my Nautilus shortcuts and I need to go into Nautilus → File System → media → 250GB to see my files. I had two folders in the drive both with backed up data, but both folder now show as files which Nautilus doesn't know what to do with them (it doesn't treat them as folders).
ls -l
reports:
...:/media/250GB$ ls -l
total 8
drwxr-xr-x 4 root root 4096 2013-01-23 19:24 2013-HOME-BACKUP
drwxr-xr-x 11 root root 4096 2013-01-23 19:22 2013-WORK-BACKUP
OK, I fixed my 250GB drive by running this command...
...and I fixed my Desktop permission problems by running this...