asterisk users - Apr 2006 - How to avoid "Avoiding initial deadlock...."

An Asterisk box at customer site shows these messages pretty regularly. This
causes one way voice, the called party cannot hear the calling party.

Apr  7 11:59:44 WARNING[18406] channel.c: Avoided initial deadlock for
'0x817b790', 10 retries!
Apr  7 14:47:46 WARNING[18406] channel.c: Avoided initial deadlock for
'0x81a4380', 10 retries!
Apr  7 14:58:53 WARNING[18406] channel.c: Avoided initial deadlock for
'0x817b790', 10 retries!

This customer is running Cisco phones, and an IAX trunk to our PSTN GW, both
using g729. The PSTN GW does not show any problems at all. The customer has
a good DSL connection so bandwidth does not appear to be an issue.

I would appreciate any input regarding this issue. I've seen several posts
recently, but no one seems to say what the root cause of this problem is.

Thanks in advance,
Joe