2768 Views 2 Replies Latest reply: Nov 25, 2010 8:09 PM by A MAD PERSON
Your antivirus or firewall is blocking the update.
"Error 20, 21, 34, 37: These errors typically occur when security software interferes with the restore and update process. If you are using a PC, follow this article to resolve this issue."
This is from Update and restore alert messages on iPhone, iPad, iPod touch and Apple TV (2nd generation)