I was facing the same issue. In order to resolve it:
Verifiy that the Java Build Path is set up correctly.
In each project right-click -> Properties -> Java Build Path -> Order and Export. Move ‘JRE System Library (jdk)’ to the top and have it check marked.
After that I did what Manimaran worte, i.e. right click the EJB project and click Validate. All the errors disappeared.
Hope it helps.