The image gallery does not show thumbnails

Dont know if this is a known issu, because a lot of people having problems with thumbnails.
I'm using Drupal 4.7.4 and the lastes image-module (25.10.2006).

My uploaded images work correctly so far. If I click on one image, it opens the image node. There I can select to view the thumbnail or the original. Both works.

All my images are organised in galleries.
But if I click on the galleries, they show all my galleries but no thumbnails of the first image in each gallery (the number of images inside each gallery is correct).
If i then click on one gallery, the gallery opens and shows "0 images in this gallery" and no thumbnails at all.
(It said before the correct number of images.)

And yes, I can direct link to the thumbnails on my server.

any ideas?

Thanks to everybody for helping in advance.

gb5256