Hi,
Are those two servers Media Servers? If they are, then you can not update the Remote Agent only, you will need to update the 10d server to version 11d.
You still can continue backing up the 10d server with the 11d server, the only thing is that you will get the error message always and will not be able to fully use the new features implemented on 11d while backing up the 10d server.
Regards,
Sandra Rodriguez
Advanced Technical Support Engineer