Problems with SIP Phone 3911 and UCCM 6.0.1

[rore]

I have problems getting my SIP Phone 3911 :s to register with my Call Manager 6.0.1. Sometimes they register and sometimes not. If the manage to register they unregister shortly. While registered they behave strange, calls are not working properly. Also, they don't upgrade with the new software. Th phones are running SIP3951.8-1-1-4, we have SIP3911_3951.8-1-2. Any ideas someone ?

[#2]

What kind of SIP proxy server you are using? And also send me the output of 'debug ccsip all' when such a disconnected call issue happens. Beware that, if the system is in production, enabling debug might affect performance of the CME.