Since you are making connections to "some" companies, this usually indicates that there are some routing/connection issues with the ones that aren't.
Have your Trading Partners check firewall rules and/or routing back to your system. Also, make sure your firewall rules are not eliminating the return communication back into your network.
The basic theory is (generally), final handshaking is not taking place for establishing the communication link. The request is being made but not receiving an "answer".