The agent push install from the ePO Server uses Microsoft networking, typically port 445. It copies over the framepkg file to the admin$ share on the target system.
So, if the admin$ share isn't available for whatever reason you cannot push out the agent.
So, first browse to \\machine name\admin$ - if not available first disable any system firewall to check this isn't the cause, then check account rights used to log on to the share, then name resolution...