sbackup still fails after Ubuntu upgrade

Hi, I am reposting (slightly enriched) the question I submitted on 11 November, then withdrew.

I was happily using the sbackup for several years without problems under Ubuntu 12.04 LTS (backing up to ext3 partition in an external drive). Then about a year ago I updated to Ubuntu 14.04 LTS, and sbackup stopped working. Each time I try to back up (ad hoc full back-up) I get after a couple of seconds the error "'NoneType' object has no attribute 'st_size'". Nothing is written in the designated log folder. There is a normally entitled back-up file, but it is unreadable and shows no properties.

Shortly after upgrading the OS, I added a second user with administrative rights, so I cannot exclude that this is the reason for the failures. I subsequently deleted the second user, but the back-up folder is still mounted in /media/[back-up partition]/[user]/[back-up folder] instead of /media/[back-up partition]/[back-up folder], but I don't see how this could be a problem.

It would be most appreciated if you had some ideas - this is a very useful package. Thanks and best wishes, John