There's always 1 image in queue, new images can't be uploaded.

When I chose "Skip upload and process the files already in your upload directory"
the uploadphoto.php will be started but stopped after a while with a blank page, and the "1 image" remained in queue.

Edit: it seems that certain images are never "processed" successfully which leads to the queue building up.
Uploading images which need little processing may not be affected.