After a time of holiday in Copenhagen [B-)] i tried again to select my surface and there it was!!! [:p] The upload via mediafire didn't work but i managed to create a picture to show what's happening:
i tried to select the surface of 1,24m² by clicking in it, but it was always the big room (walls ...

hello , my problem was not the locking of objects. after that i tried the "select all" and then "shift and select" option but that doesn't work.
my problem is that i can't select a surface that is INSIDE a room. when i trie to select it is always the wall of the room that is selected.
how do i ...

thanks for the quick response, tomorrow i trie this!

I created a room (surface) in my home but i can't select it to delete it. when i trie to select the surface, my walls are selected. i tried with the TAB button but that don't work.
thanks for your help.