What does it mean when I try to build a project and get a message box with a red "X" that says "Job failed"?

If I "configure selection", that box pops up twice. If I "build selection", that box pops up three times.

If I delete my build directory, my .kdev4 folder, and my Project.kdev4 file, I can recreate the project from the CMakeLists.txt and then everything works. This just happens once in a while, and I don't understand why. (and it is annoying to delete the project because sometimes there are many Launch Configurations setup, etc).

Any ideas?

Thanks,

David