'Install PA agent on node' failed with the following error:
SSH communication error: can not open SCP channel: Invalid ACK response from remote.
The package 'openssh-clients' is not installed on the service node.
[root@postfix ~]# rpm -qa | grep ssh openssh-4.3p2-82.el5 openssh-server-4.3p2-82.el5
Install the package 'openssh-clients' with the following command:
yum install openssh-clients
Afterwards restart the failed task.