You should try Slic3r or Cura. (I'm a Slic3r fan) Probably, you didn't get the slicer setup correctly. With Slic3r it is important to tell it what kind of printer you have so it can generate the appropriate GCode. And you need to tell it other things such as the diameter of the filament, the heat settings, layer thickness, etc.

I've never used 123-Design. But my guess is you need to export the design as an .STL file in order to use the design.

Probably, the best thing to do is just get a .STL file from Thingiverse and try slicing it with Slic3r. See if that works... Then you can try to get 123-Design going if you really want to use it.