This error message appears when the database has reached the set limit of records and needs to be purged.
These are the ways to resolve this problem:
From the Administrative Reporting Tool (ART) main menu, go to System Configuration > Database > ART Database Alert, and check Maximum number of records to see this limit. You will find the information on how to delete the old records from the database. Delete what is not needed.
You can also manually purge the Call Detail Records (CDRs). Go to the Database Purge screen > Manual Database Purge. Check if the Automatic Purge is enabled from the Database Purge screen, and the number days set there is correct.
If the CDR Analysis and Reporting (CAR) Plugin is installed, you can stop the error message or notification by opening CAR. Go to System > Database > CDR Database Alert, and set the "Notify Users when number of rows reaches" parameter to 100%.