BizTalk SMTP The part 'PartAttachment' of message 'msg_Email' contained a null value at the end of the construct block

Question

Quick summary of issue - when I set the RawString to text, the email with attachment is sent and properly named. When I set the attachment to a RawString message, I get the err

Answer 1

The following is a get-around that seems to work.

msg_Email.PartAttachment = new SBA.Ledger6002.Component.RawString(
                                msg_Raw_String.MessagePart_1.ToString()); 

If anybody can explain why I just can't set it to msg_Raw_String.MessagePart_1, I would love to know.