Since update to 1.5 all blogs login images don't show

Hi all, since i have update ultimate branding plugin to version 1.5 all blogs login images aren't showing anymore. I have been updating also to latest fixes, now im using version 1.5.3, but it doesn't fix the login images from the other blogs.

The main site its the only that shows the login image correctly, the other blogs have the url link without showing the image, and i tried also different sizes of images to see if was something related with images width or height.

Before i updated to v1.5 all images were showing ok. What could possible be?

thanks