I've just upgraded to 1.4.3.5.

My index page is a list of ALL the albums, with no thumbnails, just the album title. I have my 'album thumbnails per page' set to 999 which has worked fine before to show all the albums on one page. The 'thumbnails per row' is now set to 3 and should be on 5. However when i change any of these settings, it says its saved but it doesn't change.

any ideas?

Well, no, no ideas, but since there is no indication of what theme you are talking about, how could I have any ideas?