'check Tel Line' Message Appearing On Handset

Just replaced a Panasonic home phone system because of a "line in use" message appearing on handset. All handsets were checked with the assistance of Panasonic help service. Just replaced that system with a new Panasonic, thinking the fault was with the Panasonic hardware. Now the new system is displaying "check tel line" message. I'm sure the line connection is secure to both the Uverse server and the Panasonic base station. Any thoughts?