I encountered with the similar problem.....
Make sure that
- You create your project within your workspace. If your project is not in the default workspace where .metadata folder within which other plugin folders, and etc. will be present, then it will ask you to configure build path as the project is not build because of incomplete build path.
If the first step is clear, then go for this.....
- Right click on your project -> build path -> configure build path -> libraries -> Add libraries -> JRE system libraries -> Apply and close.