W52P - Register Failed

[Patte]

Phone: W52P
Firmware Version: 25.81.0.10
Hardware Version: 25.1.0.0.0.0.0

PBX: FreePBX
Current PBX Version: 14.0.1.20
Current System Version: 12.7.3-1707-3.sng7

Hello everyone,

I set up a W52P. At the beginning everything works fine. Than a few weeks later, my colleague told me that she is not able to call someone. I checked the settings and the registration of her user account dosen't work anymore. It's the only W52P we have but we have alot of T42Gs and one T21P.
So I tried to use the same settings on a T42G and T21P and it worked. Afterwards I tried to set my user account, which works on a T42G, on the W52P and the register failed.
I can't understand why this is happen. The network settings are the same like on T42G.
I did a reset it, but still the same problem. I did a hardware update to the latest version, no changes.

Thanks

Patte