Sip Authentication Failure 28.03.2013 22:05

Forum: Terminal Equipment

Hi,
We have 2 Cisco SPA525G2 (1 wifi & 1 Lan) and 1 SPA942 connected on 3 differents extentions.
For about a 3 weeks now, the phones often lose the registration and have difficulties to reconnect with an error (Sip Authentication Fail). When i unplug and replug the phone or wait for the next registration it register again..
This is not a router problem because the phones are connected to pbxes from differents internet access in different countries.
If you have any idea...
Thanks for your help.
Luc