Urgent ! Annoying Black line in background

Hi, I have put a grey background on my game (using BB 1.3.6) and sometimes an annoying black line appears moving from one side to another. Anyone have any idea in how can I remove it ???

 

Select your background and change the offset value > -3 is usually a good place to start

 

I also had this issue and although it may take up more memory using a separate image on each level makes better transitions