This was a downright horrible thing to do their customers.  I wondered why one of my clients hadn't paid an invoice last month.  They had been trained for past few years to receive the invoice as an attachment.  

The surprise change from quickbooks led to them not seeing invoice.  That is a horrible way to  treat customers.  We should not be surprised like this.  One more reason I absolutely do not recommend any of my friends or clients start using quickbooks.  Once you've used it for years, you have to weight this kind of crap against inconvenience of starting over.  As a potential new customer, my advice to them is to shop elsewhere.