It is completely possible to have both Honor/Memorial and eCard data elements on a donation form, the problem is that you cannot have both the "Honor Gift - Message Body" and "eCard - Message" data elements on the same donation form. This is because the message component for both of these things is actually stored in the same place in the database, so both of these data elements essentially serve the same purpose. As a result if you want to put both of these things on a donation form, just include one of those elements and make sure the donor is aware that the same field is used as the message for both the eCard and the Honor message. Unfortunately this means that if a donor chooses to use both they can only have one message that will be used for both the honor gift and the eCard, however it makes no difference which data element you use  -- The Honor Gift message element will populate the eCard message if an eCard is sent, and the eCard message element will populate the honor message if an Honor/Memorial gift is recorded.