Error while building project

When you open an existing project file (e.g. the first time you may get the following error message:

Error while building project ProjectName (target: Desktop)
When executing build step ‘qmake’

The most likely cause of this is that the build settings are invalid or missing. In Qt Creator click Projects on the left side. The Build Settings page will be displayed. In the field Edit build configuration enter the configuration you like to use (e.g. Qt 4.7.4 for Desktop – MSVC2008 (Qt SDK) Debug).