Dear Alvaro,
I believe your link is not working since it looks like the URL contains the same sub-url twice. I tried to download the files from the summary page (https://www.cbioportal.org/study/summary?id=brca_metabric), as well as from the datasets page (https://www.cbioportal.org/datasets), and both approaches work. Could you explain where on the page you try to download the files and see the error? Is it on the summary page?
I hope this helps! If you have any further questions, please hit reply all, so our continued conversation is captured by the cBioPortal Google group.
Best,
Tim