In a standard webserver, the script automatically creates categories in media and thumbnails folders each time you create a new category.
Then, each image you will upload will be sent to its category folder, and same thing when you generate a thumbnail.
It explains that you do not see your image, as the cat folder did not exist, and upload has been aborted.
I had such problem with a friend of mine hosted on an ovh virtual host, using the Plesk interface. The script was not allowed to create and set permissions to folders. Each one had to be created and CHMODed by the admin through the Plesk interface.
Try to create another cat in your 4images Admin Control Panel, and check if its folder is created. I don't think so. I think you unfortunally will have to do all the stuff by yourself.
By the way, ask your host if he can allow your script to manage folders.
