Handset problem

[KuCz]

Hello,

we have a W52P base, working with 3 handsets. Two of them works fine, but the third one is a little complicated.

So, most of the day, it works fine but sometimes it can't be called. It rings twice, then a busy tone comes up. In asterisk it says registered, and on the base web interface I can see the 3 handsets. If I reboot the base, the problem goes away.

Do you have any idea what the cause is? It's really annoying...

Thanks in advance,

KuCz