Update to ios6 when "could not establish a secure connection to device" appears (Jailbroken iPhone4)

Hi all,

I've been trying to update my Jailbroken iPhone 4 to ios6 but, unfortunately, I keep getting the "could not establish a secure connection to the device" when connecting it to iTunes. I've tried updating "over the air" but this flags up an error too. Finally, I can't restore to a previous backup because, the backups I previously had, were stored on my old (broken) computer.

Can anyone help? Any suggestions would be greatly appreciated!

Thanks,

Rakesh.