[asterisk-users] Unable to create channel of type 'IAX2' (cause 20 - Unknown)

[Joseph]

I have two asterisk servers connected via iax.
home_server <=> IAX2 <=> clinic_server

I'm just testing, calling from "home_server" via "clinic_server" but I'm getting an error message:
Call gets through to "clinic_server" but will not call back.

Dial("IAX2/home_server-957", "IAX2/home_server/218,30,rw") in new stack
[Apr 14 16:59:45] WARNING[27870]: app_dial.c:2218 dial_exec_full: Unable to create channel of type 'IAX2' (cause 20 - Unknown)
   == Everyone is busy/congested at this time (1:0/0/1)
-- Executing [219 at extensions:2] Hangup("IAX2/home_server-957", "") in new stack

This is on clinic_server:
exten => 218,1,Dial(IAX2/home_server/${EXTEN},30,rw)
exten => 218,n,Hangup

exten => 219,1,Dial(IAX2/home_server/218,30,rw)
exten => 219,n,Hangup

When somebody in a clinic server dials: 218 my phone in home_server is ringing OK
But when I call extension 219 from home server it should dial my 'home_server' 218 and it does but it gives me an error message:

app_dial.c:2218 dial_exec_full: Unable to create channel of type 'IAX2' (cause 20 - Unknown)

-- 
Joseph