If you are receiving the error message "Unable to Join Network Failure (error -3)" on the iPhone or iPod touch try this

Unable to Join Network Failure (error -3)" connecting to Wi-Fi
verify your Wi-Fi Network Name (SSID) and Security setting (WEP password, WEP hex or ASCII, WPA, or WPA2) for the device.

On the Wi-Fi Access Point/Router, you should verify if MAC address filtering is turned ON or OFF on the router, whether the security settings on the router match the iPhone or iPod touch (WEP password, WEP hex or ASCII, WPA, or WPA2), and try disabling (QoS) quality of service if that feature is turned ON for the router.

If you are still receiving the error message "Unable to Join Network Failure (error -3)" on the device when attempting to connect or join to your Wi-Fi network after trying the above suggestions, tap Settings > Wi-Fi > Other (under Choose a Network) and then enter the Wi-Fi Network Name (SSID) and select your Security setting and enter your password.