[asterisk-users] Can't connect to voip provider over NAT

[Landy Landy]

> Have you tried "nat=yes" in the
> definition in sip.conf?

Yes, I have that definition in sip.conf. Now, I'm getting the following error   

-- SIP/voipprovider-094132d8 is making progress passing it to SIP/102-09423d58
    -- Got SIP response 603 "Declined" back from 208.xx.xx.xx
    -- SIP/voipprovider-094132d8 is busy
  == Everyone is busy/congested at this time (1:1/0/0)

and I get a "This account number is not valid on the headset".

I've called my provider and they've said that everything is fine at their end. I don't know why I'm getting the message saying the account is not valid.