There is a black spring clip on the right hand side of the bobbin case that you lift up and move to the right to take the bobbin case out, if the bobbin case is coming out the spring clip might be slightly bent up, you can undo the large screw and take the clip off and bend it slightly downwards then put it back, failing that the small screws on the clip may have come loose and the spring part may not be close enough to the bobbin case.
drivewithken@blueyonder.co.uk, October 2008