asterisk users - Jun 2006 - chan_sip.c on debian testing - weird

Greetings all:

In sip.conf, I have configured an entry for Australian VoIP provider
Engin.  Sometimes, however, the following error turns up constantly

WARNING: .... chan_sip.c: Don't know how to indicate condition 9
ERROR: ..... channel.c: Unable to handle indication 9 for
'SIP/engin-5a0a'

This is followed by unreliable connectivity.

Any ideas on what I might do to fix it?

Cheers,

Michael