There are a couple of yahoo groups that might be able to help you. Other wise see the pfaff dealer for answers on this question.

Don't have a Pfaff expression 4.0 but have been sewing with Pfaffs for a number of years. The bobbins of the ones I've sewn with have to click onto a little point on the bobbin winder. I marked the point with a black marker to help me find it. If the bobbin doesn't click onto that point it won't wind correctly. Hope this helps your friend. May in Jersey

Ooh, whoops! Hope all this works out for her! I have my Exp 3.0 on lay-a-way but will also continue to use my Sidewinder. Hopefully that will avert the problem for me!

She had to take it back to the dealer twice and now it's sewing fine. Something about the take up lever having to be replaced.