If i understood the article right, it's not my task to solve the problem.
Maybe I overlooked a feature of APBackup. Is there a possibility to make a configuration to activate a 'keep alive' function? My ftp client does have such a configuration possibility.
I did not watched the clock but the transfer broke off at the same percentage of completion. Think this is really a timeout problem.
The bad thing is that I have no possibility to change the idle time on the ftp server nor on the router or the firewall