Hi Michael,
Thank you for having (very) quickly repied to my answer.
I'd prefer to generate the cache myself to prevent the user to wait
And when the user visits the site, only .thumb files are created, not .small files (they are created when the user wants to see it, and he have to wait again)
I have renamed all files from the format YYYY_MMDD_HHMMSS.JPG to the format YYYYMMDDHHMMSS.jpg
(The name of directory where the files are is "Selection" (without french accentuation))
I have deleted image cache, then I have tried to generate again.
The same problem occured (only one file . thumb in the cache).
Have you anoter indication I could try.
Thank you very much.
Jo