asterisk users - Aug 2008 - Intermittent "rejected because extension not found" On Incoming DID

I have a DID with budgetphone.nl, which has worked fine for quite some
time.  For the last few weeks, most (but not all of the time), the incoming
call does not go where it is supposed to, but instead the following message
show on the console:

[Aug 30 19:47:28] NOTICE[5161]: chan_sip.c:13865 handle_request_invite: Call
fro
m '' to extension '31203333333' rejected because extension not
found.

(NOTE: I have substituted "3333333" for the last 7 digits of the DID
for
purposes of posting.)

Here is the relevant portion of sip.conf:

[31203333333]
type=friend
username=31203333333
secret=xxxxxxxx
host=budgetphone.nl
fromuser=31203333333
fromdomain=budgetphone.nl
nat=yes
authuser=31203333333
dtmfmode=rfc2833
context=amsterdam
insecure=very
canreinvite=no
disallow=all
allow=ulaw
qualify=no
port=5060

In extenstions.conf, I have the following context:

[amsterdam]


exten => 31203333333,1,Set(CALLERID(name)=Amsterdam)
exten => 31203333333,2,Set(CALLERID(number)=3333333333)
exten => 31203333333,3,GoTo(voicepulse-incoming,5379,1)

This configuration has worked for quite some time (over a year), but only
recently has stared acting up.  What I don't understand is the intermitten
nature - I would htink it shoudl wither work, or not work.

Anyone out there have any ideas?

--Robert
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