I'm making a wing.  I did the skin first which you can see, and now I am adding the ribs.  The first picture is in the extrude screen showing the preview of the extrude, which is exactly what I want.  The second picture is the result.  It is not what I want.  The final extrude is only the left surface.  It's hard to see in the picture, but the part did not extrude- it's just the left side of the part that is there.  Only the walls of the holes extruded- sort of, as can be seen.  The weirdest thing is that it created some weird tab on the bottom sticking out of the skin.  I have no idea why it does that.  I've tried it over and over and it does it every time.

Anyone have any ideas why it is doing this?  The sketch is on a plane ane the extrude is originating from that plane.  Nothing fancy.