Ron Garret wrote:

The most likely cause is that the server is sending the wrong
"Content-type" header. Some systems can recover from this (by e.g.
letting the file extension override the content-type header) and others
can't (or haven't been configured to).

I have not too much insight into the technical details of QT, but this
explanation makes sense for three reasons.

1. If I try to watch the movie on line, the player (whichever) downloads
the whole file and displays the error mesage only at the moment when it
tries to play the file.

2. File name extensions have no tradition on Macs, so no Mac user in his
right mind would overwrite the information given within a file by this
silly three letter extension.

3. Off-line watching works, so the file data are correct.

Stefan