The directory "/path-to-programming-stuff/librarys/log4qt-install/bin/" with the compiled library is added to the project properties (PATH). This compiles but crashes at runtime with "The program has unexpectedly finished." No error message.
Ever thought about running your program in the debugger and actually seeing what's going wrong by looking at the call stack when it crashes?

It simply astounds me that people compile their programs in release mode, run it, it crashes, and then are amazed that they get a message box that tells them "The program has unexpectedly finished" with no other information. That's what compiling in debug mode and running under a debugger is for. It tells you why the program unexpectedly finished, and the answer is usually that you made a programming error that caused the crash, and the debugger usually points you to exactly the line in your code that is responsible for it.