Thanks for answers.
That was what I need: a changing-mind-hint...(I believe it isn't good english. 
)
The sensor (line-tracer-sensor DFRobot)gives a stable analog value at 0 and 1006. So I used it on an analog port.
But now I put it in an digital-port and Arduino recognized it as HIGH and LOW.
It works fine now.
Thanks...
Johan