1 - check that the credentials you use to push is a member of the local administrators group on every target machine
2 - check that port 80 is allowed from your target machine to your epo server
3 - if all else fails, install manually (or use another way of deploying - logon scripts, sms, altiris, landesk, ad etc) using a framepkg.exe agent installer
4 - last but not least: make sure all your machines are switched on / connected to the network at the point of the push