Hi, Debbie,
How these invoices were loaded? From the file or MHS/EDI message?
You can check the Installment information window (under right click on invocie header) - most probably record is there with ACH method indicated.
If invoice is loaded from file, it might be issue in file data, if from message - for some reason ACH method has been used or defaulted in the message. 
In both ways root cause is in the input data, not in the interface behavior.
                
     
                                    
            Thank you - I found that ACH was indicated under installment information.  I removed it and the error cleared.  I will have to look into the input file to see what caused it but we can move forward now.