The system is trying to write a duplicate entry into the database. The databse may be corrupt. Take a backup of the current data and run compact MASC Data.
If the error is not resolved, contact support and have a copy of your latest backup noting the date and time of that backup.
How it happens
Database corruption can occur when a power cut occurs while writting data into the database or the PC is turned off while the system is writting data to the database.