I recently started getting this error (see log below) when trying to register with the SIP server. I'm using SP4 of v11. I can receive calls but I cannot make them, I just get the same 480 error back from the SIP server. Here's what I've done to fix the issue: -Rebooted the DSL modem providing the trunk -Checked routing -Checked over all of my VOIP provider settings (nothing has changed!) -Deleted and recreated the VOIP provider in 3CX -Checked configuration against another site that is working fine using the same VOIP provider and SIP server. -Used Wireshark to see what the traffic looked like, all seemed correct. Here's the log: Code: 10-Mar-2013 11:39:49.002 Unregistered line: Lc:10000(@Group Six II[<sip:NorthGlenVillas@10.6.6.131:5060>]) 10-Mar-2013 11:39:49.002 Removed registration for  10-Mar-2013 11:39:49.000 [CM504007]: Next attempt to register Lc:10000(@Group Six II[<sip:NorthGlenVillas@10.6.6.131:5060>]) is scheduled in 5 minute 10-Mar-2013 11:39:48.972 [CM504005]: Registration failed for: Lc:10000(@Group Six II[<sip:NorthGlenVillas@10.6.6.131:5060>]); Cause: Cause: 480 Configuration error with selected binding/REGISTER from 10.6.6.131:5060 10-Mar-2013 11:39:48.972 Updating device Dev(1):[sip:NorthGlenVillas@10.6.6.131:5060 / NorthGlenVillas]: No update on error responses: SipResp: 480 tid=5e77087ada2e4d07 cseq=REGISTER / 1 from(wire) 10-Mar-2013 11:39:48.829 [CM504003]: Sent registration request for Lc:10000(@Group Six II[<sip:NorthGlenVillas@10.6.6.131:5060>]) I'm working with our VOIP provider but it's been since Friday morning (48 hours downtime!!!) and they haven't been proactive at all in helping me.