Error Code Yellow/Fast Flash

VoIP lines encountered problems during registration with SIP proxy server.

? What Causes This

Internal communication failure, service outage for VoIP or provider-specific issues.

Ensure correct configuration: check user credentials/phone numbers in gateway's settings.
Confirm your home phone network is not interfering with installation (check for compatible adapters).
Reboot the hardware and contact AT&T customer support if issue persists.

Source: page 18 of the official manual

From the manual

This error code appears in: