I have a setup with a router running OpenWRT with an openvpn client.

Windows 7 pc's cannot access the vpn. They time out trying to access servers on the VPN. The mystery to me is that the setup works fine for my laptop running ubuntu. I can access the VPN without any issues.

I previously had a router running Tomato with the same openvpn setup and all the computers could access the VPN.

What could account for the difference in behaviour? Is there something I am missing in the OpenWRT setup that is required for windows networking that is on by default with tomato?

To clarify the OpenVPN client is on the OpenWRT router. The client connects to the OpenVPN server. But when I try to access the VPN from Windows computers on my network I cannot.