### Please describe the problem.
In a usb drive with a repository in direct mode, when I converted to indirect mode it fails

### What steps will reproduce the problem?
cd /Volumes/usb
git annex indirect

### What version of git-annex are you using? On what operating system?
git-annex version: 4.20130627

### Please provide any additional information below.

[[!format sh """
openFile: resource busy (file is locked)
failed
git-annex: indirect: 1 failed
"""]]