I'll have a word with Phil admin, but I think it's because the threads were moved from another source and the pics didn't move with the posts; possibly because of a software difference, vbulletin to xenforo?
Just spoken to Phil and it looks as though some of the attachments didn't come across with the posts and are not available now.
If anyone comes across a thread where the missing picture is a vital part of it, can you please let me know?
Thanks, Chris