Won't slice my stacking models

[samsonnetje 0]

I would like to stack the following objects to see if this works. But Cura is unable to slice. Not sure what to do here. 

[gr5 2,247]

Strange.

1) What is that huge black rectangle with the curved edges?  I'm thinking that is part of your STL files?  That might have something to do with it?

2) Please get to this state as you show and then do menu "file" "save project as" and post that file so I can see what you are talking about.  Also what version of cura are you using so I can test with the same version.

3) Did you check the 3 comments listed in your post?  A) try selecting everything (ctrl+A maybe) and scaling everything down by 3X to see if it can then slice.  It might be the black area extends beyond the edge or the printer.  B) Make sure an extruder is enalbed C) Is it possible you modified these 3 objects to be modifier meshes?

[Cuq 206]

You are in mode print : One at a time. What's why you have this message ( and the Huge black rectangle) notice by @gr5