Security :: Ssh Authentication With Rsa - Error Permission Denied (public Key)

I have trouble with rsa authentication:

I did create an rsa certificate with ssh-keygen using my root account on a client: ssh-keygen -t rsa -b 2048 no passphrase I did copy the rsa pub_key from my client to the server scp id_rsa sampleuser@sampleserver:/home/sampleuser/.ssh/authorized_keys

I did change the ownership to the "sampleuser" of the pub key file on the server: I trayd to connect:
ssh sampleuser@sapleserver

I get that: permission denied (public key)... I know I do smth wrong but I don't know what.