"All Circuits Are Busy Now"

When dialling from one asterisk box to another I am getting the error “All Circuits Are Busy Now”. This has just started occurring yesterday.
This is what I get on the dialing box; asterisk1*CLI> -- Executing Macro("SIP/555-af3131d8", "dialout-trunk|2|479||") in new stack -- Executing GotoIf("SIP/555-af3131d8", "1?3:2") in new stack -- Goto (macro-dialout-trunk,s,3) -- Executing Macro("SIP/555-af3131d8", "user-callerid") in new stack -- Executing GotoIf("SIP/555-af3131d8", "0?report") in new stack -- Executing GotoIf("SIP/555-af3131d8", "0?start") in new stack -- Executing Set("SIP/555-af3131d8", "REALCALLERIDNUM=555") in new stack -- Executing NoOp("SIP/555-af3131d8", "REALCALLERIDNUM is 555") in new stack -- Executing Set("SIP/555-af3131d8", "AMPUSER=555") in new stack -- Executing Set("SIP/555-af3131d8", "AMPUSERCIDNAME=Test Ext") in new stack -- Executing GotoIf("SIP/555-af3131d8", "0?report") in new stack -- Executing Set("SIP/555-af3131d8", "CALLERID(all)=Test Ext <555>") in new stack -- Executing NoOp("SIP/555-af3131d8", "Using CallerID "Test Ext" <555>") in new stack -- Executing Macro("SIP/555-af3131d8", "record-enable|555|OUT") in new stack -- Executing GotoIf("SIP/555-af3131d8", "0 > 0?2:4") in new stack -- Goto (macro-record-enable,s,4) -- Executing AGI("SIP/555-af3131d8", "recordingcheck|20100225-111350|1267096430.128641") in new stack -- Launched AGI Script /var/lib/asterisk/agi-bin/recordingcheck recordingcheck|20100225-111350|1267096430.128641: Outbound recording not enabled -- AGI Script recordingcheck completed, returning 0 -- Executing NoOp("SIP/555-af3131d8", "No recording needed") in new stack -- Executing Macro("SIP/555-af3131d8", "outbound-callerid|2") in new stack -- Executing GotoIf("SIP/555-af3131d8", "1?start") in new stack -- Goto (macro-outbound-callerid,s,3) -- Executing NoOp("SIP/555-af3131d8", "REALCALLERIDNUM is 555") in new stack -- Executing Set("SIP/555-af3131d8", "USEROUTCID=") in new stack -- Executing Set("SIP/555-af3131d8", "EMERGENCYCID=") in new stack -- Executing Set("SIP/555-af3131d8", "TRUNKOUTCID=") in new stack -- Executing GotoIf("SIP/555-af3131d8", "1?trunkcid") in new stack -- Goto (macro-outbound-callerid,s,11) -- Executing GotoIf("SIP/555-af3131d8", "1?usercid") in new stack -- Goto (macro-outbound-callerid,s,13) -- Executing GotoIf("SIP/555-af3131d8", "1?report") in new stack -- Goto (macro-outbound-callerid,s,15) -- Executing NoOp("SIP/555-af3131d8", "CallerID set to "Test Ext" <555>") in new stack -- Executing Set("SIP/555-af3131d8", "GROUP()=OUT_2") in new stack -- Executing GotoIf("SIP/555-af3131d8", "0?108") in new stack -- Executing Set("SIP/555-af3131d8", "DIAL_NUMBER=479") in new stack -- Executing Set("SIP/555-af3131d8", "DIAL_TRUNK=2") in new stack -- Executing AGI("SIP/555-af3131d8", "fixlocalprefix") in new stack -- Launched AGI Script /var/lib/asterisk/agi-bin/fixlocalprefix -- AGI Script fixlocalprefix completed, returning 0 -- Executing Set("SIP/555-af3131d8", "OUTNUM=479") in new stack -- Executing Set("SIP/555-af3131d8", "custom=IAX2/restdale") in new stack -- Executing GotoIf("SIP/555-af3131d8", "0?16") in new stack -- Executing Dial("SIP/555-af3131d8", "IAX2/restdale/479|120|Tr") in new stack -- Called restdale/479 -- Hungup 'IAX2/restdale-6' == Everyone is busy/congested at this time (1:0/0/1) -- Executing Goto("SIP/555-af3131d8", "s-CHANUNAVAIL|1") in new stack -- Goto (macro-dialout-trunk,s-CHANUNAVAIL,1) -- Executing NoOp("SIP/555-af3131d8", "Dial failed due to CHANUNAVAIL") in new stack -- Executing Macro("SIP/555-af3131d8", "outisbusy|") in new stack -- Executing Playback("SIP/555-af3131d8", "all-circuits-busy-now") in new stack -- Playing 'all-circuits-busy-now' (language 'en') -- Executing Playback("SIP/555-af3131d8", "pls-try-call-later") in new stack -- Playing 'pls-try-call-later' (language 'en')
Can anyone help?

On further investigation it appears all of a sudden none of the boxes in my company can dial this one specific box… nothing to my knowledge has changed on it. and it can dial out via other boxes… any ideas anyone?