I right tried to upload an image to use in a post, but it was not accepted because the following error:

Failed to upload image; the format is not supported

The image was a JPEG; I also tried with a PNG image, but I got the same error. I then noticed the URL started with https://, tried with http:// but I got the same result.

Are there other restrictions that are applied? This is the first time I have such an error.

This is the image I am trying to include: http://drupal.org/files/project-images/path_breadcrumbs_settings_page.png.