I want to create a letter to my clients that, as an option, will list any Invoice records with open balances. At this time, when there are no invoice records for that client, the layout in preview mode is blank. Is there a way to have the layout display the other content even if there are no invoice records?

FYI - I have an invoice layout that optionally lists checks written on behalf of the client. This layout displays the other content even when there are no check records.

You can't print or preview 0 records. There is, however, a print option to print a blank record. Depending on what the "other" stuff is, and so long as you don't need to see this on the screen, you could have those with no invoices do a find all (or find any record, it doesn't matter since it won't print) and then print a blank record.

HTH