you probably have different title updates
the way i do it was i connected my jtag hdd to my retail xboxs, and updates mw2, then connected it back to my jtag
and from what ive heard, you dont need the same dashboard revision, but i have the same one anyways lol
go to network settings and go to test xbox live connection
if your jtag is not banned, it might ask you if you wanna send some information or something, go to no. and check if the connection loading thing goes past modem, and starts connecting to the internet.