Not a nice title, not a nice error as well…
I encountered this error while trying export/import a file through the object model.
Searching the net I found some posts suggesting this could be caused by the versioning in the Style Library. As soon as you've checked-in multiple major versions of a file the error 'could' occur. But that had to do with Incremental deployments.
MS has a hotfix for that case: http://support.microsoft.com/kb/936867.
But I was not doing any Incremental deployments, I just wanted to export one single file from a site. Also, I did not have the time to request, wait and install the Hotfix so I tried something else:
Delete all content from the Style Library, and it worked.
Just a cut-and-paste everything to your local machine, refresh the browser (just to be sure) and put everything back in place. Of course you will lose any version data, but thats a fair trade-off.
The issue is also related to the Site Image gallery and other site-level-galleries, so you might want to try resetting them as well.
koning53