Acknowledgee Letter cannot be used as a merge condition in Honor/Memorial Acknowledgement Letters
Choose to create one letter per gift instead of per tribute:
1. Open the gift record and select the Tribute tab 2. Open the tribute 3. Select a letter for the acknowledgee 4. Run the Honor/Memorial Acknowledgement Letters again 5. On the Fields to Include tab, double-click constituent information 6. Double-click letter. The letter is now available to use as a condition.