I have flash v188.8.131.52 installed as well and it works fine. CTL+F5 if it didnt work and you did not get a popup message. If it still doesnt work and you get no message then I'm sorry, I don't know what to tell you.
All of the problems, based on your descriptions, sound related to issues with your browser. Perhaps someone can speak with you in french and get a better, more detailed translation to english.
neophil, I'm told by the network guys that we are experiencing a situation right now whereby you may be getting shuffled between different servers on each request to the forums. This causes a problem with caching. You can determine this by the 'balsaXX' label at the bottom of the page. I'm told that we wont have this resolved until early next week our time. This may be causing issues where an upload appears to have succeeded, and then upon refresh no image appears. The only way to tell for sure is to watch that label at the bottom. If it changes between refresh, then that could account for what you're seeing.
Beyond that, keep looking for client/browser problems on your machine. I'm still working on this, and will continue to do so until we have it solved.