SSH refused on RHEL 5.4

The server was up and running and no recent change or upgrade was done.
configuration on pair server is identical however only the SSH connection on db2 is refused, and ssh on db1 is working.

[oracle@to5uspdb1 ~]$ ssh -v 10.128.36.19
OpenSSH_4.3p2, OpenSSL 0.9.8e-fips-rhel5 01 Jul 2008
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 10.128.36.19 [10.128.36.19] port 22.
debug1: Connection established.
debug1: identity file /opt/oracle/.ssh/identity type -1
debug1: identity file /opt/oracle/.ssh/id_rsa type 1
debug1: identity file /opt/oracle/.ssh/id_dsa type 2
debug1: loaded 3 keys
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3
debug1: match: OpenSSH_4.3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(102410248192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
Connection closed by 10.128.36.19
[oracle@to5uspdb1 ~]$

xxx# ssh root@to5uspdb2
key_load_public: invalid format
ssh_packet_read: Connection closed
xxx#

what is the solution and how we can apply since there is no ssh access.

thanks,