T48 on FritzBox - redail calls from FritzBox-AnsweringMachine messages

[OptoInspect Netzwerkservice GmbH]

Hello to the Forum,
I had an T48S working great on a FritzBox7490.
One Problem is that we can't redail recorded calls on the answering machine inside the FritzBox. If we hear the message and press "3" for redail, we have a busy Signal. If we contact the answering machin from a normal analoge phone, it works. So I think, some configuration issue on the T48S
Have you any idea?

Greetings from Berlin!

Detlef