Hi,
i recreate this issue and the problem is that you have inverted normals. Choose polygons and press ctrl+N. The screenshot that you attached, you can see that the faces are black and that means that the faces are looking to the wrong direction. Also important is to remove dublicate verteces and apply the scale of your model.
The order matters. First object mode, ctrl+A -> scale to apply object scale. Then edit mode, select all, W -> remove doubles. Then ctrl+N to make normals consistent and pointing out, which might not work if you have mesh errors that prevent it from working.
And yes, don’t crop screenshots and provide a .blend with questions. Tutorial linked in my signature tells more.
thank you very much for your help and sorry for the missed blend file.
you routed me on the right way…it was the normals directions.
A “recalculate normal” solved the problem.
In fact I’ve used the Bridge command to make the hole.