If you build the sample application in qfacebookconnect-qfacebookconnect/sample and the library is located in libqfacebook-build/debug it will fail in just this way.

Change the reference in your Makefile to ../../libqfacebook-build/debug/libqfacebookconnect.so and it might work better.

And when I talk about "invocation of the compiler", I really mean every line that starts with g++ that you get after typing "make". If you look at this line, you'll see every flag that is passed to the compiler and you can see where it will look for files.

This bad habit of hiding the actual compiler invocations is a detriment to software development. It's bordering to ******ed to hide this with some misplaced idea about "protecting" the user from the output. Read the documentation and try to find the switch that will turn off silent compilation.