I have had the same problem with sending statements to customers, majority have no problems but some cannot open the attachment or the attachment is not there when sending thru "Send Forms". Last summer  when this began, I was initially told it had something to do with Microsoft and QuickBooks. However if that was the case it would be all - so that was bull___ line. Then I was told it was QuickBooks and Apple products.

After playing around, I came up with a fix to be able to email the customers their statements. I remove the emails from the Send Forms list for the customers that are unable to view the attachment and then process the remaining. I then save a pdf file of all statements and pull out each statement for the other customers and email them separately. 

It is a pain, but the customers are happy. It would be nice if there was a complete fix to this, especially for the amount we pay for the software.