I am at a loss (and have lost over 6 hours of my life trying to find a solution). I successfully upgraded my iPhone 4 to iOS6 last week. Yesterday morning when I attempted to upgrad my iPad 2, I ran a back-up and when attempting to upgrade to iOS6, I received a "1604" error message.
Now the iPad is in recovery mode. I have tried all of the following:
When rebooting and having the iPad connected, the computer will successfully install the Apple driver (as indicated in the Device Manager) but once iTunes starts, it will recognize an iPad in Recovery Mode, extract files, and during the "preparing iPad for recovery" phase, it will run for a long time then I receive the "1604" error. Looking back at the Device Manager, the Apple driver is now flagged with the yellow "!". I have also forced the commuter to find the appropriate driver and it states that it is up to date.
I am running Windows Vista 32. iTunes and all Windows related products are up to date.