iOS users know that the best place to get content for their iPods, iPads, iPhones etc is the iTunes Store. It houses Applications, Games, Music, Videos for purchase, Free download or trial versions.
To get access to the iTunes store requires a username / Password authentication referred to as "Apple ID" - Each apple ID can be used on the iTunes store to authorize Only 5 Computers for purchase.

If you're new to this: I'm talking about Downloading Content from the iTunes Store with your computer and Transferring that Game / Application to Your iDevice Via USB cable SYNC. This is where you need to authorize that computer to sync apps to your device.

Over the years I've exhausted my 5 Computers Authorization Limit, forgetting to De-authorize them most times. So it was no surprise when i Installed iTunes on a New Computer and was denied access to Sync apps. - SOLUTION? - De-authorize all Computers from your Apple account. Here's how:

• Open iTunes and Sign in, then click on your account email - Top-Right of the screen.
• Click Deauthorize all and Confirm.

That's it. You can now authorize your new computer to sync applications to your iDevice.
NOTE: The De-authorize All option is only available when you've used all 5 authorizations for your account and can only be used once every 12 months.