Polygon to be split crosses

[Electra102]

Hello folks using Brother  PE11 to manually edit print photo. When I get to( select image, shapes) Split outline, when I use mouse to outline a shape, sometimes it works but others a window opens.        ! The polygon to be split crosses itself.

            Edit the polygon so the lines do not cross.

I really can't work out what I'm doing wrong. Can anyone help? Many thanks

[diver361]

Please attach a screenshot to understand problem