Keyboard-row qwertzuiop[ partwise not working

Dear Apple Users,

the top of my keyboard-row (letters q to [) does not work all time. I have tried all kinds of tips given by apple support site, but the problem keeps coming back.

Sometimes it helps changing the languages of the keyboard, but sometimes this way doesnt solve the problem as well.

Time to time I am lucky and the complete keyboard is working. The strange thing is, that all of the other keys do work without any problems at time while the first row isnt.

It is a Macbook Air Mid 2011 with 1,8Ghz i7 and 4 GB RAM.

Does anyone have any conclusion or tips?

Thank you!