I did what this guy says and after rebooting the phone(connected to pc via usb and KIES started all time of this process), after the phone rebooted windows 7 installed a new driver (samsung phone modem driver). After this it synced automaticly with KIES. Happy to upgrade this bad boy to ICS !!
Good luck to everyone having problems with their GS2.
Originally Posted by axesever
I had this problem, here was my fix:
Plug the phone into the USB.
Turn phone off, hold lock and select Turn Off.
After its off and loads the Battery Charging icon, turn it back on.
It should send the driver info to the computer and recognize it.
If it doesn't work for you, it might be because I enabled USB debugging prior to restarting it. It works in Kies now.