To: safenoglio@hotmail.com
This happens due to the following circumstances. Obviously, the duration of your images is set to 5 sec or so, am I right? If this is the case, the maximum transition duration can be set to 2.5 sec. The transitions work the following way: they make pictures intersect with each other, so if you apply transitions between images which last for 5 sec, a part of the first image gets intersected with the part of the second one, so the maximum transition duration can make up the half of the image duration which is 2.5 sec.
What you can try therefore, is settings duration of the images to 8 sec. This way you will get 3.999 sec duration for transitions (a split second is needed for the changing).
Regards