What browser are you using?
You said, that previous creations worked - did you change the browser between creation processes?
If you would recreate your previous, working soundset (either make a copy, rename it and try to upload again, or recreate from scratch and try to upload again) - does that work? If not, can you recall, what changed on the computer youâre working with?
Oh, and another thing: you did the restart procedure, all right. Have you deleted to files in the according folder, too?