Unlike iTunes error 3194 or error 4014, iTunes Error 9 is not a very common error code. But when it hits, whatever you were trying to do is stopped. In most cases, Error 9 comes up when you are trying to upgrade/update your firmware.
Like most error codes, there are a variety of fixes for iTunes error 9. What may work for someone might not work for you. What you’ll need to do is try out all the possibilities.
How to Fix iTunes Error 9
Hardware vs Software
Apple’s support page lists error 9 as a possible security software issue. This could be firewall blocking access to specific websites/web resources (like iTunes trying to download something from Apple’s servers). Some other websites (and users who’ve found some solutions) note this error as happening due to hardware issues (faulty cable, faulty USB port, accidentally disconnect etc.)
We’ll try to fix error 9 through both these options.
One of the first things you can try is to change the USB port where the cable connects. This is too basic, I know, but you’d be surprised at how randomly this fixes all hiccups when trying to upgrade/update the firmware.
If you can access another computer / laptop with iTunes installed, the second thing you can try is to update/upgrade your iDevice on another computer. Yes, this is another basic thing to try.
Cable Disconnect / Faulty Cable
When the cable is unplugged/loose, the iPhone looses connection with iTunes. This leads to a plethora of errors (different numbers) and it looks like Error 9 (while not documented on Apple’s support page) could also be one of them.
Security / Anti-virus / Firewall
This is where it gets all about software.
If you’ve set up firewall or connecting through proxy/vpn, you should make sure that this is not preventing iTunes from connecting to Apple servers remotely. When you try to upgrade your iPhone/iPad, iTunes connects to Apple, checks for hashes, security keys etc. (a bunch of stuff that it uses to verify that your iPhone or iPad is technically “updatable/upgradable.”)
If sometime during the attempt, iTunes is stopped from connecting to Apple’s servers, it throws an error. Error 9 is a rarity even then (more common is Error #2 and Error #16xx). But still, since it’s documented, you must try to fix your firewall settings.
Different OSes and different setups have different configurations for proxy or firewall. You might have to tweak them so that all servers are accessible.