I am using ActionBarSherlock as a library project in a project which is a library itself. It was all working fine until I moved the project to a new computer and updated the
Here is simplest solution:
Right click on your project folder -> Build path -> Configure build path -> Add External Jars(From libraries tab) -> select "android-support-v4.jar" file.
(It'll be located in Android SDK folder here is generic path "android-sdk\extras\android\support\v4").
After this clean you project and happy coding...