As I've commented to Christian Kirbach in private mail, when I generated the reports before a new stable release, I didn't get this kind of errors, so I'm really confused about what is happening. The only difference I see is that I used to generate them under Ubuntu 12, and now I'm using Debian... maybe it's due to Python versions? I'm installing a virtual machine to investigate it...
Anyway... simply ignoring the translator-credits line would be enough to have good reports. Media links are not used at all in the PO files, so it doesn't matter how you translate them; about placeholders, they should placed in the right place, as they often indicate the kind of license or the name of the program, so they should be, at least, the same in the translated and in the original string (but not in the same order....).
Thanks to all of you for your comments (and special thanks to Ask for taking care of this :) )
