All host unreachable

What happens if you add this to your ansible.cfg?

[ssh_connection]
control_path = %(directory)s/%%C

Maybe your control_path gets to long (being set to
ansible-ssh-%h-%p-%r) and thus you run into the BROKEN PIPE error.

Just a guess.

Can you use adhoc commands?

ansible -m ping foobar (for the host foobar)

Johannes