The Problem is caused by mksdcard not being installed correctly.
if you are running 64 bit, do this to fix the mksdcard problem.
sudo dpkg --add-architecture amd64
sudo apt-get update
sudo apt-get install libncurses5:amd64 libstdc++6:amd64 zlib1g:amd64
and 32 bit:
sudo dpkg --add-architecture i386
sudo apt-get update
sudo apt-get install libncurses5:i386 libstdc++6:i386 zlib1g:i386
In SDK 6.0, the error message is different but means the same thing.
Unable to run mksdcard