Okay, that's the problem: Imprudence does not support mesh. You need to install another viewer: Singularity, Cool or firestorm to upload meshes. I don't know exactly the current configuration of simonastick. Maybe you want to try NweWorldStudio too
http://newworldstudio.net/en/downloads/ . It uses the same base as Sim-on-a-stick, but it is a bit easier due to the Interface. You find a lot of tutorials here:
http://forum.newworldstudio.net/viewforum.php?f=4. Please try to get another viewer working with your distribution and feel free to ask again, maybe I can send you an iar-file with the NPC-script and instruction.