Multilink Callback (ISDN) with Cisco3640

#1 Hi,

I try to configure a multilink callback on a cisco3640 to windows 2000 clients.
The client should dial, the router should callback while opening the second ISDN channel. But this fails !
Callback on only one channel works, but the client receives a timeout while waiting for openning the second channel.

Here some information about Router's configuration:
[...]
ppp callback accept
ppp authentication chap
ppp multilink bap
ppp multilink idle-link
ppp bap call accept
ppp bap call request
ppp bap callback accept
multilink max-links 2
multilink min-links 1
multilink load-threshold 16 either
[...]

What's wrong ?
I hope somebody can help me.

Regards,
Marco