Many are calling this a bug in the iTunes Store system related to the "mature content" warnings Apple uses on Apps with a 17+ rating. Apple Discussions user "ecasadei" reports:
I'm getting the same error. I have 97 app updates available, and when I try to "Download All Free Updates" at once, a window pops up stating "IMPORTANT: This product contains material that may be objectionable to children under 17. By proceeding, you are confirming that you are 17 or older." and then I get an error message stating that iTunes could not complete my request because an unknown error (414) occurred. I have no idea which of these apps has been given a 17+ rating -- at first glance they all seem pretty tame -- otherwise, I'd update those manually and then try to download the rest all at once again. As it stands, I'm forced to update them all one by one. I've also seen the following error appear when I try to get an update on some individual apps:So the general consensus here is to download your 17+ rated Apps one at a time and save all your others for a mass download. It would also be helpful to download your updates for applications before too many build up in your queue. You can update many of your applications directly from your iPhone and download updates on your computer even if your iPhone is not plugged in. While it does not appear that the recent update to Snow Leopard directly addressed this issue, watch for the next iTunes update to tackle the problem (and we will let you know if it does).MZCommerceBuy.AgeCheckFailureKey.addToCart_message MZCommerceBuy.AgeCheckFailureKey.explanationThere's clearly some sort of bug in the age verification process during app updates. Frankly, I don't need Apple to babysit me with regard to my App Store purchases. I'm hoping that the popup asking me to confirm my age is part of this bug, and that it's not something I'll be forced to do every time I want to update a 17+ app. That would be a little ridiculous.