asterisk users - Mar 2004 - Dropping voice to exceptionally long queue

Hi,

We experienced a problem this week on our asterisk box (ast-2) that has 
a T1 coming in and talks over IAX2 to a second Asterisk box (ast-1). In 
the current setup we use ast-2 for outgoing phone-calls only, it takes 
calls (over IAX2) from ast-1 and routes those calls out over the T1.

This morning ast-2 would print out the following error message (1124 
times total):

Mar 25 04:51:07 DEBUG[163851]: Dropping voice to exceptionally long 
queue on IAX2[asterisk-001@asterisk-001]/16385

After that it would no longer be possible to make outbound phone calls. 
Ast-1 showed the IAX2 connection to the crashed/hung ast-2 as 'timed 
out' (instead of 'registered'). In contrast to that 'iax2
registry show'
on the hung ast-2 would still show the IAX2 connection as 'registered'.

The exact same thing happened 2 days ago where ast-2 printed the above 
error message about 800 times before hanging.

We had to killall -9 asterisk on ast-2 (because 'stop now' would hang 
indefinitely) and restart it. After that ast-2 would immediately 
re-register with ast-1 and everything would start working again.

Any pointers of what's wrong here?

Regards,
Markus