Registeration Error

I’m stuck in the initial phase of registering my softphone “X-Lite” with asterisk box. my sip.conf is given below

[general]
context=default
srvlookup=yes

[100]
type=friend
user=Asim Arif
secret=100
qualify=yes
nat=no
host=210.2.144.221
canreinvite=no
context=internal

and its giving me the following error
"Registeration Error:404-Not found"

Kindly help me out so that i could move ahead.
Your valuable comments are highly appreciated.

what are you trying to do with: user=Asim Arif
Are you trying to set the CID ? Also do you get any errors with the phone registering or just when trying to make a call ? What do you have in extensions.conf ?

Thanks a lot for the reply but my problem luckily has been resolved. Yea i was trying to register my softphone with asterisk box. The mistake was that i wrote host=mymachineip instead of writing host=dynamic n defaultip=mymachineip.
Anyways, thanks again for all of your help. This forum is really helpful for me.