You *must* have the plib version 1.0.19 or later installed on your system to build the FGFS simulator!" You can get the library from: http://www.woodsoup.org/projs/plib/ Build notes: You should be able to just run "./configure" to configure the package and use all of plib's defaults. Then run "make" followed by "make install". By default, plib installs itself into /usr/local/plib/ which is where flightgear now expects to find it.