SVN Error Message "Cannot replace a directory from within"
This is just quick Google-bait as I received the following error when trying to export from SVN:

svn: REPORT request failed on '/!svn/vcc/default'
svn: 
Cannot replace a directory from within

In my case it seems to have happened due to the fact that the directory I was trying to export didn't actually exist (good old case-sensitivity).

Executing a svn ls ... on the URL in question gave the somewhat more helpful message:

svn: URL '...' non-existent in that revision