ssh failure on ubuntu 16.04

Am new to ansible and cannot seem to get the very basics started.

ANSIBLE VERSION

ansible 2.3.2.0
config file = /etc/ansible/ansible.cfg
configured module search path = Default w/o overrides
python version = 2.7.12 (default, Nov 19 2016, 06:48:10) [GCC 5.4.0 20160609]

CONFIGURATION
OS / ENVIRONMENT

Ubuntu 16.O4

SUMMARY

ssh works OK from the host control machine, however when I use anisble i get the error below.

used same credentials to login.

12.5.18.14 | UNREACHABLE! => {
“changed”: false,
“msg”: “Failed to connect to the host via ssh: Connection closed\r\nConnection to 12.5.18.14 closed by remote host.\r\n”,
“unreachable”: true
}

Your control machine is Ubuntu 16.04, but what is your target machine
12.5.18.14 running?
And what do you see when you run the playbook with '-vvvv'?