Backup files with rsync: error 23

Question
I'm trying to make a backup of my /home to transfer all data from one computer to another. I wanted to save the backup on the same computer and than transfere it to another one
i've run in terminal:

sudo rsync -avz /home/maria /home/guest/backu

and I had as the result:

sent 58797801 bytes  received 23050 bytes  4705668.08 bytes/sec
total size is 100202958  speedup is 1.70
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1060) [sender=3.0.7]

I have no idea, which files were not transferred, what makes the whole backup useless for me?