Ahhh, how is your network set up?
If the computer running the ICS (the main computer) is shut down or restarted, that can cause the other computers to lose connection. I'm not an expert in this field but this could be the case. I'd like to know the answer to this as well.
Just found this: http://compnetworking.about.com/od/w...ectiondrop.htm
Hope that is of some help, maybe #3.