This error occurs when WPA security is enabled either on the PS3 system or on the Wireless access point (router) and WPA security isn't enabled on the other device.
Restart the PS3 system and try to connect again.
Contact the person who maintains your network to find out whether the network uses WPA security then correct the settings in your PS3 network settings. Click here for a walkthrough on setting up your network configuration.
If your Wireless access point (router) filters MAC addresses, you will need to register your MAC address. Contact your router manufacturer to find out how to do this.