Cannot transfer incoming calls

[EverythingVoice]

Good morning all

We have a Unify OpenScape Business S with 5 W52P handsets connected. They register fine, they can call out and receive incoming calls but I have a slight issue...

If an incoming call is answered, the user cannot transfer this call. You can place on hold (but the caller receives no music on hold), dial another user, press the transfer option and the call disappears from the handset but never goes anywhere.

By contrast, if the cordless initiates an outbound call, hold, recall, transfer etc etc works fine.

Base unit firmware is the latest on offer: 25.81.0.10

Any ideas?

Thanks in advance

Richard