Hi filarono,
Your issue is very different to the one this topic is regarding. However, the issue in the following topic closely relates to yours:
http://wordpress.org/support/topic/backup-keeps-failing-email-says-it-didnt?replies=9#post-3358205
Could you please go to the topic and install the diagnostics version mentioned in my second post in that topic? It will produce a log file that you can email to us for investigation, then we should be able to locate the issue and find a workaround or a fix for you.
Please post any responses into the above topic and not this one, it will help keeps things tidy and organised and easier for people to find solutions to their problems if the issues are kept all in one place!
Thanks,
Jason