This is probably be if the tables you've linked to are not always populated but are linked with an INNER join instead of a LEFT OUTER. When you use an INNER join but there isn't a record on the other end then the whole query returns nothing.
To check how they are linked just open the table diagram in Crystal and double-click on each of the lines between the tables.
Thank you so much! That was it! I can now see the data in my print views.