I am currently seeking more about this, but I have some bits that may help.
1. When we got broadband through our cable provider (Comcast), we were sold a single user license even though we were explicitly connecting two computers.
Upgrading to a multi-user subscription (for up to 5 connections) solved that.
2. I'm currently trying to configure 4 computers to connect. I have noticed that if a configuration for one has WPA and another has WPA-2 they will bump. This may be true for differences in WEP-keys, TKIP setting, etc. If you do new configurations, the settings may revert each time to a default, which you may not notice. Keeping the network settings matched may help. Using a portable memory device to run a saved configuration on each machine can improve their synchronization. Unfortunately, one computer is a notepad with no USB slot. Still working on that.