Turn off your Wi-Fi wait 10 sec then turn it back on, if that don't work restart your iPad by holding down the on/off and home buttons until you see the Apple logo.
You can also try reseting the network settings on your iPad
Settings>General>Reset>Reset Network Settings
This will erase all stored wifi networks, so you'll need to try and connect to your network again.
Other reasons for getting a 169 address are: Using the wrong security key when connecting, issues with the wireless router (try another reboot on the rotuer), and wireless interference.