The content you download from PlayStation®Store can be played only on the devices that have been activated. There might be limitations on the number of devices per Sony Entertainment Network account that can use the content downloaded from PlayStation®Store. The type of content determines the number of devices that can be used. System activation usually happens automatically when content is downloaded, but when the limit on the number of devices would be exceeded, it is necessary to deactivate any excess devices.
You can activate or deactivate your PS Vita system using this menu item.
When signed in to PlayStation®Network, tap [PlayStation®Network] > [System Activation] and follow the on-screen instructions to activate or deactivate the system.