Okay. I figured it out. I had to download FFTW again and recompile the libfftw.a and libfftw.so library again (http://fftw.org/download.html and http://www.fftw.org/fftw2_doc/fftw_6.html)
One has to to compile and install it in the following way:
./configure --enable-shared
sudo make CFLAGS=-fPIC
sudo make install
Fixed.