In cases where the phone had been properly working for a long time and is only suddenly afflicted with these error messages, a network power cycle is often able to clear it up.
Other helpful network troubleshooting:
- Swap out the Ethernet cord connecting the phone to the network for a different one (to see if a faulty cord might be the issue).
- Is the phone connected to a wall jack? If so, try connecting it directly to a networking device (router or switch).
- If the phone is connected to a networking device, try plugging it into a different port on the device (to see if a faulty port is the issue).
- If accessible, review the firewall/router settings and be sure to disable the following:
You can also try setting a static IP on the phone, which has been known to help resolve these issues.