Error after Android Support Library to version 21

At 17 October 2014 Google release Android 5.0 as Android API 21. As an Android developer, I promptly to download and applying it to my applications and update all of my . Because all of my applications depends on AppCompat I also update the Android Support Library to version 21. FYI, I use eclipse Juno as my main IDE.

After updating the AppCompat, all of my applications getting some error. Trying to go back to Android Support Library version 20 to get them working again but fail because there is no turning back to version 20 after updated.

Fortunately, the solution is very simple. Just open the project.properties for the AppCompat project folder and change the target value to android-21