Rsync over ssh with root privileges

[Stayvoid]

Hi,

I'm trying to copy some files from a remote server.
(That server uses passphrase to auth users.)
Rsync should be able to copy files with root privileges.

Here is my attempt:

sudo rsync -avP --exclude 'proc' --exclude 'dev' --exclude 'tmp'
--exclude 'sys' --exclude 'mnt' --rsync-path='sudo rsync' -e "ssh -t
-t -i /home/USER/.ssh/key" USER at SERVER:/  /mnt/backup/

Response:

protocol version mismatch -- is your shell clean?
(see the rsync man page for an explanation)

The following file is empty:

ssh remotesystem /bin/true > test.dat [1]

Any ideas? Am I using the correct syntax?

Thanks

[1] http://rsync.samba.org/FAQ.html