The project was not built since its build path is incomplete. Unknown Java Problem

The project was not built since its build path is incomplete. Cannot find the class file for java.lang.Object. Fix the build path then try building this project error.

To solve this missing class problem. Right click on project properties, change from Android 4.03 to Android 3.1. The eclipse will automatically add the library back. Latter change back to Android 4.03. This is due to incomplete Eclipse shut down.