I use the jAlbum uploader already 10 years to upload albums to my Stratoserver, but I can't remember that I ever had seen this error message, so I guess there is recently someting changed which causes this problem.
You are adding the album http://www.andrewolff.nl/FotoSerie/Klompenpaden/ but the server redirects to https://www.andrewolff.nl/FotoSerie/Klompenpaden/ . This is probably new behavior by your server.
The add album function doesn't follow redirects, so that's why it fails. We could add that but currently haven't. So currently you need to tell jAlbum that the URL starts with https.
java.io.IOException: Error while adding album. Server reported: java.io.IOException: Image data does not represent an image.