If you are using Visual Studio for building your project, why are you also using Qt Creator? Stick with one or the other. I use Visual Studio (only) along with the Qt VS plugin for all of my Qt projects. The only thing I use Qt Creator for is to build and run the demos that come with Qt, and that only because I don't want to be bothered creating a Visual Studio project for them.

Why are you putting LIB, DLL and EXE files into the VS project? What do you think Visual Studio (or Qt Creator for that matter) is going to do with them?

By the way, if you are using Visual Studio to build your own project, any LIBs or DLLs also have to be built by the Visual C++ compiler. If your Qt Creator kit is using mingw, anything compiled in Qt Creator will be incompatible with code built in VS.