For some days my avatar links are broken

Hi There,

For some days all my avatars links for users and blogs are broken. I can upload avatars, but I only see a broken link. During these days I updated and installed some plugins, but deactivated most of them without change.

The link from the broken avatar images is:
The link that would work is:

As I am digging in the dark I wonder if you have any hint for me what to do?