Could you please verify the version of your libavcodec and libavutil libraries?
You can do this by listing files in their install directory, e.g.:
$ ls -l /usr/lib/libav*
Currently NoMachine supports avcodec library up to major version 55. If you have the newest version (which is 56), you should downgrade your libraries to use it with NoMachine. Support for version 56 is being added.