An "Apple expert" replaced the battery of my macbook air last week. To fix the new battery there are a lot of screws, but one is just behind the space tab. The person who did it made a mistake and used a screw too long that press the space tab from inside and create a deformation, making the space tab to loose sensitivity. When this key doesn't work writing is the ##$*! I opened the mac myself following the ifixit instructions, discovered the problem and changed the screw for the correct one: problem solved! I hate the Mac technical support in Barcelona I love ifixit Wish my experience will help someone