You will need to grant permissions within System Manager:
Open Synergy Client.
Go to System Manager.
Select Options.
Expand Common and click Security.
Within here, the user mentioned either does not have permissions or is not specified.
The user needs access to:
System Manager.
Select Options.
Find Admissions.
Click on Mail Merge.
Find the Child Letters Directory value.
📌 Note: This directory should be shared.