"Unknown Error" when trying to rig imported model

Hi
So I tried different ways, but still get this error.
originally i used rigged .blend file, set skeleton in rest position, combined all the parts into one, set scale, rotation, etc.. at 0 and export as .fbx (try all the same with .obj - no difference) without rig bones, model it self (probably important?) 
I am worried that model is not in the center when imported, so i need to place markers manualy (yes, it always "hits" the model, but I suppose that could be the reason of an error) 
perhaps the error occurs due to the fact that the model has gaps? is it fixable?
Thank's for the help 
my future projects are in danger... 😞