I think it is something different, file permissions again? rep-cache.db permissions, the usual culprit, looks ok (we have a cron job now that should fix them all every hour).
I just retried this one and I got the same error! I can only surmise that it is a bug in svn itself. Only idea offhand: would you mind checking out a fresh copy of the repository (or just the directory with the problematic file ... what is it, btw?) and trying again? Maybe it is something problematic embedded in the current checkout, somehow. We can also try recreating the repository (svn dump | svn load), though whether that will help ... Most of all, we should poke around to see if there is anything on the net about it. Thanks, Karl