I have a customer who had multiple power surges. Once the 7100 came back, the extensions did not register on the phones. They are however able to make and receive calls using the shared lines appearances. The extension lines show up as xxxx on both buttons. The button map in the web interface looks to have the correct extension scheme, but they can not make internal calls. Why are the extensions not showing up, and what can I do to change that?
The most common problem with an extension failing to register is a password mismatch between the NV7100 and the IP phone. Under the Voice-->Stations-->User Accounts page in the GUI, try editing one of the extensions and on the General tab click the Generate random password button (see image below). Click Apply and then reboot that phone to have it try and register again.
If that does not resolve your issue, try grabbing the debug output from "debug sip stack message" from the CLI when you reboot one phone.