Hi Eva,
I am glad that you solved your problem. Please note that when my (language didactics) students author Hot Potatoes exercices I advise them to never ever use "strange" characters in the names of their HP exercises and picture or audio files.
Characters allowed: a-z, A-Z, 0-1, -, _ (i.e. hyphen and underscore)
Forbidden: é, à, ç, ù, etc. and, of course, all punctuation characters and blank space.
Fortunately (or unfortunately), Windows is all too permissive and most Windows users have taken the habit to use the whole range of their keyboard characters, including blank spaces to name their files. But when these files are zipped, uploaded to non-Windows (Unix, Linux, etc.) servers and unzipped there (as is often the case with Moodle installations), problems occur with files named using the "forbidden characters".
Hope that helps,
Joseph