I was recently working with SVN and somehow a directory got fubar’ed and I was getting that message when trying to commit.
The resolution was to do a fresh checkout in a temp directory, then TAR up the .svn folder for my fubar’ed directory and copy it over to my current SVN workspace. I had to make sure I still added any files that were not added in the other .svn folder, but that was no problem and my issue was resolved!