Sometimes the flash uploader does not work.
- Check the write permissions for images/stories/ directories and subdirectories (Try to change permissions to 777)
- Check if your flash player version is upper to 7 (Update to newer version)
- If your PHP version was patched with suhosin (Add in your .htaccess, php.ini or suhosin.ini the next line: suhosin.session.encrypt = Off)
If the problem persist you can deactivate the flash uploader in the Main Configuration Settings and use the traditional and safe form uploader.