### Please describe the problem.

While dropping 19 unused files from an annex, I got this error:

    error: invalid object 100644 c873416e78db4dd94b6ab40470d6fe99b2ecb8bd for '002/0a6/SHA256E-s427690--03aeabcde841b66168b72de80098d74e047f3ffc832d4bbefa1f2f70ee6c92f8.jpg.log'
    fatal: git-write-tree: error building trees
    git-annex: failed to read sha from git write-tree

I've actually seen this before, a few months ago.

### What steps will reproduce the problem?

I have no idea, but once it happens I can't interact with unused files anymore.  Also, `git annex fsck` now reports this same problem as well.

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

git-annex version: 4.20130815, OS X 10.8.4

> [[done]]; no indication this is anything other than a corrupt git
> repository, which can be caused by system crash, disk data loss, 
> cosmic rays, etc. This is why we keep backups... --[[Joey]] 
