The AOSS button will be found on one's wireless router and not on his PlayStation Portable. AOSS stands for AirStation One-Touch Secure System and is a system that allows a network connection to be established with the push of a button. Please refer to your router's manufacturer for further information.
A router that has a WPS button will sometimes also establish an AOSS connection. If an Internet connection - AOSS error message appears on your PlayStation Portable, go to Wi-Fi Settings under Network and retry AOSS, restart the application, and restart the system. If the error persists, contact your router's manufacturer.