[Asterisk-Users] Call disconnects after 30 minutes

[Eric Alexander]

We have been experiencing a strange problem lately. Calls are disconnected
after approximately 30 minutes when dialing out through a T100p. Asterisk is
disconnecting the calls and logging the following: 

full:May 12 14:03:35 DEBUG[1970]: Bridge stops because we're zombie or need
a soft hangup: c0=SIP/sipuser-a58d, c1=Zap/9-1, flags: No,No,No,Yes 

Asterisk version: 1.0.7 

My Zaptel.conf:
loadzone = us
defaultzone=us
loadzone=us
defaultzone=us
span=1,1,0,esf,b8zs
bchan=1-9
dchan=24

I have google'd and wiki'd but cannot seem to find any info on this problem.
Anybody else had this problem?