Many times SSH key auth issues come down to incorrect file permissions. Make sure your servers have the correct permissions listed below.
On the source server (where you're connecting from):
.ssh directory: 700 (drwx------)
public key (.pub file): 644 (-rw-r--r--)
private key (id_rsa): 600 (-rw-------)
your home directory should not be writeable by others (at most 755 (drwxr-xr-x)).
On the destination server (where you're connecting to):
All of the above, as well as:.ssh/authorized_keys must be: 600 (-rw-------)
