Permission denied (publickey).

We have Sophos UTM in an Active/Passive configuration. When i SSH to the master i should be able to connect to the slave with the command: ha_utils ssh.

When i do this on the master (with root) it says the following:

Connecting to slave
Permission denied (publickey).

I have 2 clusters, and both are giving this issue. I recon it is some configuration setting which i need to change, can anyone help me with this?

Thanks in advance.