Thanks so much for looking at this straight away – it works now! I’ve just done two test collages, one from Flickr and one from my computer and both worked. There are still a couple of glitches, e.g. when I try and change the colour of the border to white, the cursor drags and it takes a few attempts, and the way the squares now split into top, middle and bottom make it a slower process (I just want to put one photo in each square) but I’m so glad I can save them now.
Thanks again 🙂