We have found that Word throws this error when the first Fund ID in your database file is alphanumeric (contains both letters and numbers). To resolve this,
  1. Open your fndgift.txt and fndgrant.txt files in notepad. 
  2. Change the first Fund ID to contain only letters and save the document. 
  3. Run through the process of inserting the databases for your gift and grant detail as per the instructions. It should complete successfully. 
  4. Lastly, reopen the fndgift.txt and fndgrant.txt files and change the first Fund ID back to what it is supposed to be. 
Once you have successfully inserted the coding for your gift and grant detail, the merge should run smoothly without need for adjusting the Fund IDs going forward.