The code includes a null div.. <div id="slideEnd"></div>. It appears that Kompozer corrects the code and assuming that a null div is superfluous, it deletes it. But the previous and next buttons fail to work without it. I got around this by adding <br> in the div.
As quite a few tools now do self correcting of code this change could save many a lot of hassle.
(I do not understand why the slideEnd div is required, as it is not referenced anywhere. I would be grateful if someone could educate me and explain why this div is necessary to the working of the code)