First of all qmake -project should only be done once when you start working on a project. It creates a template for the project file, which then should be updated manualy. The error you experience is probably because you run qmake -project on a directory which already contains files generated by moc and these file are added to the SOURCES group but they shouldn't. So either make distclean before running qmake -project again or modify the project file yourself (which is the way to go).