Polycom does not recognize Hangup() command!

Hi,

I use a test system for Asterisk release 1.4.21.1 with the same dialplan I use on a production system with Asterisk release 1.2.24.

The Hangup() command is not properly recognized from my Polycom phones under the 1.4 release.
After the hangup no sip channel is open anymore on the asterisk server 1.4,
but my Polycom phones still have a busy line on the phone so that I have manually end the call.

When I use eyeBeam for example, it works as expected.

Any help is really appreciated.

Thanks, Bernd

It belongs to the second line, different server, I use on the phones.
If the phone only use one sip registration it works!