Yesterday I was trying to do a merge in a svn repository using a command like:
rado@ubuntu-laptop:~/svn-wc/$svn merge svn://somehost.net:3690/some/very/long/path svn://somehost.net:3690/some/other/very/long/path
just to get the really strange error - "svn: Cannot replace a directory from within".
After reading through mailing lists messages, bug reports and anything else I could find about this error there was no enlightenment.
In the end the cause turned out to be a simple typo in one of my very/long/paths.