C20 with status registration retries expired

[Batuhan Kilic]

Cisco C20 codec status show this registration retries expired error. Callsetup mode is gatekeeper, ip is correct, id correct, portallocatin dynamic.

Working normal but suddenly this happened. What can be the problem? 

[Batuhan Kilic]

changing dns server solved the problem

[Patrick Sparkman]

Probably tried to re-register to the gatekeeper and couldn't resolve the address with previously configured DNS server.