I would consider the following things:
The constraints and force are not connected to the solids (non design), since they are attached to free points. This will be the reason for the error message.
All longitudinal and vertical inner beams are modeled twice
There are a lot of intersections and so it is a problem to find clear contacts for the solver. You get a warning message before the run (in my version 2017.3)
At all, try to model a flat solid plate between the two non design borders. Then you get a idea on how a optimized support structure looks.
After clean up point 1 and 2, I could do a structural analysis (see attached picture). I did not try to perform an optimization, since it is useless for me.