Thanks for the answers.
Maybe useful for others: after some nights warming my head, the problem was solved. I had made an "update" of Internet Explorer, from version 5.0 to 6.0. This new/modern/improved version doesn't have Java components (and Mr Gates didn't warn me), so I had to get this from another source. It is a small example of unavoidable pain caused by conflicts between technical and commercial areas. This is not a complaint or surprise either ; it's just a statement of a reality. For our purpose here I can guess how much migraine similar things are causing and will cause to digital photographers.