This error occurs when you run the Transactions - Dunning Cycle Letters or Transactions - Recreate Dunning Mailmerge process in A4W if the list of merge fields exceeds 255 characters for one or more of the dunning cycle letters.
Note: This limitation is due to Microsoft Office, not A4W.
So, you should edit the dunning cycle letters in the Reporting - User Defined Reports - User Defined Letters screen to remove some of the merge fields used in the dunning letter document or fields that are selected but not used in the letter.
You can "print" individual letters for a client to test if there's an issue with the dunning letter document by following the below steps:
Open Care Episodes - Care Episodes and Assessments screen in A4W.
Select a client who was included in the dunning cycle.
Click the Assessments tab, then choose their most recent assessment.
Select the Completion tab.
Click the Reports button, and a new screen will appear.
The top pick list will be set to Hard Copy by default, but change it to Dunning Letter.
Select the Word button to open the Select Dunning Letter screen.
For the Letter to Use option, choose a letter used for the dunning cycle.
Click the Merge button to print output the letter to Microsoft Word.