Sometimes, Eclipse may have errors in calculating build paths, which may result in that some projects are marked as red cross error icons and further building is interrupted. The common error message for this would be “Project … is missing required project …”.
Try to check out and make sure that there are no errors. But try to clean and rebuilt the project do not clean out that error mark? Please try to close the project, and then re-open it, clean and rebuilt the project. It may help.