asterisk users - Sep 2006 - inbound call from GSM gateway: handle_request_invite: Failed to authenticate user

Hi all,
I am getting a "handle_request_invite: Failed to
authenticate user" error when I attempt to receive
calls from a GSM gateway (I can successfully call
through the device VoIP-GSM from asterisk).
I have looked for a solution to this error but most
point me to adding a register line which I've tried
(or probably my syntax may be wrong) without success,
below is an extract from the CLI, below that is my
sip.conf 

<CLI>
Use EXIT or QUIT to exit the asterisk console
    -- Registered SIP '2006' at 192.168.0.100 port
5060 expires 60
    -- Saved useragent "CMI CM5K" for peer 2006
Sep 15 18:11:02 NOTICE[19600]: chan_sip.c:10468
handle_request_invite: Failed to authenticate user
"+27729932161"
<sip:2006@192.168.0.100:5060>;tag=3ed9e889
</CLI>


[general]
context=from-sip                        ; Default
context for incoming calls
                                ; if asterisk was
compiled with OSP support.
                                ; defaults to
"asterisk"
                                ; Realms MUST be
globally unique according to RFC 3261
                                ; Set this to your
host name or domain name
bindport=5060                   ; UDP Port to bind to
(SIP standard port is 5060)
bindaddr=0.0.0.0                ; IP address to bind
to (0.0.0.0 binds to all)
insecure=very
srvlookup=yes                   ; Enable DNS SRV
lookups on outbound calls

;register=>2006:XXX@192.168.0.100:5060

[authentication]





[2008]
type=friend
username=2008
secret=XXX
context=from-sip                ; Where to start in
the dialplan when this phone calls
host=dynamic
defaultip=192.168.0.12
port=5061
insecure=very
canreinvite=yes

[aaron]
type=friend
username=aaron
secret=XXX
context=from-sip                ; Where to start in
the dialplan when this phone calls
host=dynamic
defaultip=192.168.0.12
insecure=very
canreinvite=yes

[myAGI-app]
type=friend
username=myagi_app
secret=XXX
context=from-sip                ; Where to start in
the dialplan when this phone calls
callerid=XXX
host=XXX



[2006]
insecure=very
type=friend
username=2006
secret=XXX
context=from-gsm                ; Where to start in
the dialplan when this phone calls
callerid=XXX
host=dynamic
defaultip=192.168.0.100
dtmfmode=rfc2833






[2001]
type=friend
username=2001
secret=XXX
context=from-sip                ; Where to start in
the dialplan when this phone calls
callerid=XXX
host=dynamic
defaultip=192.168.0.11
                                ; No registration
allowed
dtmfmode=RFC2833                ; either RFC2833 or
INFO for the BudgeTone

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