Communication is extremely important for a successful outcome. Each member of a team should know that they must communicate if they have any issues where they cannot make the deadline. If you have a unresponsive member, the first thing you must do is to reach out to them through e-mail or by phone. If that method fails, the PA should personally set up a meeting with this person and discuss any issues. If members cannot meet up at a single time than a conference call should be set up or a group email should be sent out regarding the latest updates/news. I agree with cdj24 that if you try all these methods and the member is still unresponsive than you should ask for them to be removed.