Image trace doesn't work properly (for svg)

Hello I am trying to convert my image and save it as a  svg (to be used in Videoscribe) with Image trace. When I do so, the lines are not recognised, only the white spaces in between te lines (so forms)...So instead of one thick line I get two very thin lines and a sort of watermark image.  If I need to do all the images by hand (with extra layers) it does work but costs a lot of time.

So can anyone help me to solve this? thanks!

Ingrid