Make sure your router is updated to the latest firmware.
If that doesn't help, try disabling the password for your network temporarily. If that works, the people who make your router will need to update the firmware for newer 802.11.X devices. This same issue happens for some routers with every new phone release, both iOS and Android. Some routers never get updated to work, others will. That depends on the company who made it and its age. If not using a password "fixes" it, you can try switching from WPA2-AES encryption to TKIP encryption -- but know that TKIP is far less secure and will affect performance of your router over time, requiring frequent reboots. But it's better than open WiFi. You'll find all the information you need about encryption and how to change it in your router manual.
If that doesn't work, I'm out of ideas.
Edit: This is because both iOS (BSD-based) and Android (Linux-based) use an open-source WiFi stack and it's regularly improved from version to version. Improvements often equal compatibility issues, unfortunately.