I just checked post #4 from the link you provided.
Yes you do have two pics per file and it did work.
My guess is the resolution of the files (the size); perhaps those other files were just smaller enough to fit?
I did try to cut one file (with two shots) right @ the edge of the speakers, but it was still too large; that's when I separated the two pictures.
My composite pictures are not too large. I never exceed 1.2 MB (I always compress my images). The image posted here, for example, is 1.5 MB:
https://www.whatsbestforum.com/threads/keithrs-dream-speaker-search.27069/page-10#post-554162
I guess the problem is that the images that I want to post are composite (even though the end result is simple jpeg files). The old composite images were transferred from the old WBF, but now I cannot use the system anymore.