Strange "page not found" error in register

When I enter in this part of my drupal based webpage http://www.tabernil.com/secciones/audio/algo_personal I always receive some strange warnings in the register, the error says:

Page not found - secciones/audio/img/s.jpg

It's true that this JPG doesn't exist but I never had it and I also can't find any reference to it in the link above, so I don't understand where this error message comes from. Has anyone any idea of what can be going on?