ipod touch v 2.0.2

i restored my ipod touch to 2.0.2, then i jailbroke it with Quickpwn.
but i cant connect it with my itunes now. when i plug in the usb a box appears "iTunes could not connect to the iPhone ***because an invalid reponse was received from the device"
what should i do? i cant even downgrade it now.
btw it's iTunes 7.7.1.11.