OOPS.. major screw-up!!! ...i'm such an ass!
flex was missing on my system, because I installed a minimal system. During the installation of CentOS i always choose "Minimal" to get a lean clean machine!
After that I build the system peace by peace... and because of that, flex is not installed from the get go...
I usually have my own notes, on how I install my systems... and forgot to look at them before I started this thread.
Sorry for this mistake... CASE CLOSE (he said in shame)