Thx for the help suggestions!
Did as you suggested... what happens here is that the selected polygons (with locked selection and without aswell) do NOT show up when I get to skin editor and open the skin I want... the selection however is visible IN the earlier selected skin (which i would want to get rid from). So I can´t edit or choose the skin I want - it´s like preterminated because i once chose wrong skin.
In a smaller cube model I made the changing of skin worked well... dunno what has happened. I think this is some error with the groups. As suggested before I tried to MERGE GROUPS to try to get rid of this problem... did not help! :-(