Does this apply to your situation?
For example, if you've exported a repository as <Location /www/foo>, but you've also set your DocumentRoot to be /www, then you're in trouble. When the request comes in for /www/foo/bar, apache doesn't know whether to find a real file named /foo/bar within your DocumentRoot, or whether to ask mod_dav_svn to fetch a file /bar from the /www/foo repository. Usually the former case wins, and hence the "Moved Permanently" error.
Can you post your SVN Apache vhost configuration here?