scott: Do you have suggestions on how I can handle this?
I do! First up there is a little confusion on the Invoice table because there is already a CustomerType field but it doesn't appear on the Invoice screen so it's not used. What you want to do is pull in the CustomerType from the Customer table - this field is set on the new customer screen under addition information. To do this you first need to link the CustomerType from the Customer table to the Invoice table.
Open up your table list and click the Invoice table then add a linked field using the Customer table on the CustomerType field. You will have to use a display name other than CustomerType since this is already in the table (but not used).
Once you make that link, this field will be available in the report designer.
~C