Which database file did you import your data into? I'm guessing that you imported the data into a copy of the Contacts template that comes with filemaker. When you import data into this file, you should enable the Auto-Enter option so that each imported contact receives a ContactID serial number. Without this serial number, as you've discovered, parts of the system won't work.
You'll need to either reimport your data into a new copy of the contact manager while enabling this option or you'll need to use Replace Field Contents to give each imported record a serial number ID and also to update the next serial value settings. (Replace field contents has an option that updates this for you.)
Yep, that did the trick! Thanks a lot.