According to the iPhone wiki:
Error 14:
Custom firmware update fail (PwnageTool until 4.0.1). You have to restore the device with a custom firmware. Update to a custom firmware isn't working. Device isn't bootable. 2
USB Problem. Check the USB connection and try other direct ports or maybe the USB cable is an older one. Device isn't bootable.
You're trying to 'update' to a beta firmware instead of performing a restore. Device is still bootable if you kick it out of recovery mode.
Rebooting your Mac or PC may resolve this issue.
Root file-system partition size was set too small in the ramdisk's options plist.
Error 21:
Custom firmware restore fail (PwnageTool since 4.1). You have to put your device into the DFU mode and not into recovery mode. Device won't boot correctly an stuck at the Apple logo after the error. Press and hold power and home button until it reboots.
Error when using Sauriks server for a restore with iOS 5.x in the recovery mode at least on a A5 device.
This error can also happen when you try to restore an iPod with hardware dfu. Use iREB r5 to solve this.
You are trying to update to a beta firmware without UDID activation.
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I think there are some errors in your iOS system files. So read this guide to fix the problem.
How to Fix iTunes Error 14
crwdns2934271:0crwdnd2934271:0 GwenStefani crwdne2934271:0
change your pc try on another pc or try on laptop, I also got the same error I just tried on laptop and the problem was fixed :)
crwdns2934271:0crwdnd2934271:0 ahsanayaz509 crwdne2934271:0
1. Turn off Security Software
2. Hard Reset your iPhone
3. Reboot your PC
4. Check your USB Cable
5. Update the latest version of iTunes
More:
http://bit.do/e3fFu
crwdns2934271:0crwdnd2934271:0 NikkiBella crwdne2934271:0