Neil,
I think it's the photo that you have to rename. When I get that message, I go back one page, copy my text to the clipboard (so I don't have to retype it), then close the Landracing forum and just reopen it. Go to your photos (I keep my downsized photos in separate file), open them up and "save as" by adding a 1 or a 2 to the end of the file name, making sure the size of each photo is less than 100 kb. Then I can paste my message in the reply box , add the newly named photos, and it seems to accept them.
Tom