How do I get rid of the creases that appear along the axis of relefction when using the mirror modifier?
Does ist help if you place the Mirror-Modifier on top of all the other modifiers?
Activate the do clipping button and make sure that the vertices along the mirror axis cross the mirror access merging them together with their mirrored pendants eliminating the crease. If you still see a crease after this operation make sure that the mirror modifier is above the subsurface modifier and that there are no two edgeloops close to the mirror axis causing this crease.
BTW it is always a good idea to show a image of the problem.