Project Builder -- duplicate class error


I'm writing a Java application in Project Builder in the form of "Java Tool," which creates a Java Archive of the project. For some reason, my project can't compile due to a "duplicate class" error for one of the classes. I checked all my package and class declarations to find that I made no mistakes. Has anyone seen this problem before? Thanks and take care.
No. What class is it complaining about? What happens if you change the class name, will it compile then?