Asterisk: Unable to create channel of type ‘DAHDI’ (cause 34 – Circuit/channel congestion)

Strange issue started with our Asterisk install yesterday.

When dialling out via ISDN BRI the call fails and the following error is logged:

Unable to create channel of type 'DAHDI' (cause 34 - Circuit/channel congestion)

I have restarted the server, checked the config files and confirmed with the Line Provider (BT) that there is no fault on the line.

Incoming calls work perfectly and so does dialling out via PSTN line.

Really could use some suggestions if anyone has any ideas?

dahdi-channels.conf:

; Autogenerated by /usr/sbin/dahdi_genconf on Thu Oct  9 10:05:01 2014
; If you edit this file and execute /usr/sbin/dahdi_genconf again,
; your manual changes will be LOST.
; Dahdi Channels Configurations (chan_dahdi.conf)
;
; This is not intended to be a complete chan_dahdi.conf. Rather, it is intended
; to be #include-d by /etc/chan_dahdi.conf that will include the global settings
;

; Span 1: XBUS-00/XPD-00 "Xorcom XPD #00/00: BRI_TE" (MASTER) AMI/CCS 
group=11
context=from-zaptel
switchtype = euroisdn
signalling = bri_cpe_ptmp
channel => 1-2
context = default


; Span 2: XBUS-00/XPD-01 "Xorcom XPD #00/01: BRI_TE" AMI/CCS 
group=12
context=from-zaptel
switchtype = euroisdn
signalling = bri_cpe_ptmp
channel => 4-5
context = default


; Span 3: XBUS-00/XPD-10 "Xorcom XPD #00/10: FXO" 
;;; line="7 XPP_FXO/00/10/0 FXSKS  (In use) (no pcm) (SWEC: OSLEC)"
signalling=fxs_ks
callerid=asreceived
group=0
context=from-zaptel
channel => 7
callerid=
group=
context=default

Section from the dialplan:

[from-trunk]                ; just an alias since VoIP shouldn't be called PSTN
include => from-pstn

[from-pstn]
include => from-pstn-custom     ; create this context in extensions_custom.conf to include customizations
include => ext-did
include => ext-did-post-custom
include => from-did-direct      ; MODIFICATION (PL) for findmefollow if enabled, should be before ext-local
include => ext-did-catchall     ; THIS MUST COME AFTER ext-did
exten => fax,1,Goto(ext-fax,in_fax,1)

And the Debug log for PRI with verbosity set to 127 and Debug set to 50…

localhost*CLI> originate dahdi/g11/01234567890 application playback demo-congrats
1 -- Making new call for cr 226
    -- Requested transfer capability: 0x00 - SPEECH
1 -- Restarting T203 counter
1 > Protocol Discriminator: Q.931 (8)  len=31
1 > Call Ref: len= 1 (reference 98/0x62) (Originator)
1 > Message type: SETUP (5)
1 > [04 03 80 90 a3]
1 > Bearer Capability (len= 5) [ Ext: 1  Q.931 Std: 0  Info transfer capability: Speech (0)
1 >                              Ext: 1  Trans mode/rate: 64kbps, circuit-mode (16)
1 >                              Ext: 1  User information layer 1: A-Law (35)
1 > [18 01 81]
1 > Channel ID (len= 3) [ Ext: 1  IntID: Implicit  Other  Spare: 0  Preferred  Dchan: 0
1 >                        ChanSel: B1 channel
1                          ]
1 > [6c 02 21 83]
1 > Calling Number (len= 4) [ Ext: 0  TON: National Number (2)  NPI: ISDN/Telephony Numbering Plan (E.164/E.163) (1)
1 >                           Presentation: Presentation allowed of network provided number (3)  '' ]
1 > [70 0c a1 30 37 37 34 37 36 30 33 36 32 33]
1 > Called Number (len=14) [ Ext: 1  TON: National Number (2)  NPI: ISDN/Telephony Numbering Plan (E.164/E.163) (1)  '01234567890' ]
1 > [a1]
1 > Sending Complete (len= 1)
1 q931.c:3637 q931_setup: call 226 on channel 1 enters state 1 (Call Initiated)
1 -- Restarting T203 counter
1 -- Restarting T203 counter
1 < Protocol Discriminator: Q.931 (8)  len=7
1 < Call Ref: len= 1 (reference 226/0xE2) (Terminator)
1 < Message type: CALL PROCEEDING (2)
1 < [18 01 89]
1 < Channel ID (len= 3) [ Ext: 1  IntID: Implicit  Other  Spare: 0  Exclusive  Dchan: 0
1 <                        ChanSel: B1 channel
1                          ]
1 -- Processing IE 24 (cs0, Channel Identification)
1 q931.c:4405 q931_receive: call 226 on channel 1 enters state 3 (Outgoing call  Proceeding)
1 -- Restarting T203 counter
1 -- Restarting T203 counter
1 -- Restarting T203 counter
1 -- Restarting T203 counter
1 < Protocol Discriminator: Q.931 (8)  len=12
1 < Call Ref: len= 1 (reference 226/0xE2) (Terminator)
1 < Message type: DISCONNECT (69)
1 < [08 02 82 81]
1 < Cause (len= 4) [ Ext: 1  Coding: CCITT (ITU) standard (0)  Spare: 0  Location: Public network serving the local user (2)
1 <                  Ext: 1  Cause: Unallocated (unassigned) number (1), class = Normal Event (0) ]
1 < [1e 02 82 88]
1 < Progress Indicator (len= 4) [ Ext: 1  Coding: CCITT (ITU) standard (0)  0: 0  Location: Public network serving the local user (2)
1 <                               Ext: 1  Progress Description: Inband information or appropriate pattern now available. (8) ]
1 -- Processing IE 8 (cs0, Cause)
1 -- Processing IE 30 (cs0, Progress Indicator)
1 q931.c:4558 q931_receive: call 226 on channel 1 enters state 12 (Disconnect Indication)
1 -- Restarting T203 counter
    -- Channel 0/1, span 1 got hangup request, cause 1
1 NEW_HANGUP DEBUG: Calling q931_hangup, ourstate Disconnect Indication, peerstate Disconnect Request
1 q931.c:3435 q931_release: call 226 on channel 1 enters state 19 (Release Request)
1 -- Restarting T203 counter
1 > Protocol Discriminator: Q.931 (8)  len=8
1 > Call Ref: len= 1 (reference 98/0x62) (Originator)
1 > Message type: RELEASE (77)
1 > [08 02 81 81]
1 > Cause (len= 4) [ Ext: 1  Coding: CCITT (ITU) standard (0)  Spare: 0  Location: Private network serving the local user (1)
1 >                  Ext: 1  Cause: Unallocated (unassigned) number (1), class = Normal Event (0) ]
    -- Hungup 'DAHDI/1-1'
1 -- Restarting T203 counter
1 -- Restarting T203 counter
1 < Protocol Discriminator: Q.931 (8)  len=4
1 < Call Ref: len= 1 (reference 226/0xE2) (Terminator)
1 < Message type: RELEASE COMPLETE (90)
1 q931.c:4490 q931_receive: call 226 on channel 1 enters state 0 (Null)
1 NEW_HANGUP DEBUG: Calling q931_hangup, ourstate Null, peerstate Null
1 NEW_HANGUP DEBUG: Destroying the call, ourstate Null, peerstate Null
1 -- Restarting T203 counter

Thank you.