Model has unexpected Overhang in Slic3r

Hi All, im quite new to Sketchup and 3D Printing.
Now my model looks great in sketchup, looks level and all.
but Slic3r detects overhang on places i didnt expect.

can anyone help?

Attached is my model, STL fileblinker full with cutouts.skp (1.2 MB) blinker full with cutouts.stl (147.9 KB)

and slic3r screenshot

Try to make it a Solid Group, as it should for 3D printing

Thank you for your reply @mihai.s. Unfortunately the same error is still there

blinker 2.skp (1.2 MB)
Try this one. Is it any different?

Thank you sir, that solved the problem.
May I ask what you changed?

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It was not aligned with the main axes and of course, it was not a Solid Group.

:open_mouth: i should have noticed that myself :frowning: thank you so much for your help!