Is this on Eclipse? Apparently something is getting in the way of your resources being compiled. This happens quite a lot. Some tips from my experience:
1) Changing verbosity settings for the Android builder, in preferences. Then you can check console for resource generation errors.
2) Sometimes the resource generation doesn't give good errors. For example if you changed the res directory structure into an illegal one it sometimes will fail without a proper error. Compare your project to a working project.
3) Sometimes the Eclipse Android plug-in seems to be stuck in a broken state, an Eclipse restart usually works.