Try the following steps in order until the issue is resolved:
  1. Ensure that each honor/memorial's constituent record has an acknowledgee.
  2. Add tribute a to the gift(s).
  3. Open the appropriate tribute. Mark the Ackn? column to acknowledge the tribute. Select Not Acknowledged in the Acknowledge drop-down.
  4. Ensure that the query includes the acknowledgee rather than the constituent who gave the gift. Or if selecting to include one record, select the acknowledgee record.
  5. Ensure that the address on the acknowledgee's relationship record is marked to Send mail to this address
  6. If running a conditional mail merge based on letter code, be sure to use Hon./Mem. Acknowledgee Letter and not the Gifts.Letter field.
  7. Recreate the custom Honor/Memorial Acknowledgement Letters parameters set.

If the issue still occurs, refer to How to troubleshoot missing or incorrect records in a mailing (labels, envelopes, Quick Letters, etc.).