You must actually own a directory in order to set its access and modification times to an arbitrary value. Just having write permissions is not sufficient.
Either chown the directory, or don't use the -t or -a flags in rsync (-a includes -t). Note that this will have a small performance penalty since rsync will no longer be able to detect unmodified files and it will perform additional checking to see if they are different.
(courtesy http://lists.samba.org/ar...13709.html )