I was trying do model simple box with opened top for 3d print. I added plane, extrude the edges in Z axis and applied solidify modifier. The model looks fine, however the Cura cant slice it properly (it slices only the bottom). I really dont understand, what I'm doing wrong, because as soon, as I extrude something, it immediately gets unsliceable. Could somebody provide me a hint, on what to focus? File is here: Cube
Update: I do use the 3d print addon, you can see it on the screenshot from blender.