Thanks for the time taken to develop the plugin. I have noticed that the plugin fails on my site after a number of backups. It seems to me that it is estimating the size of backups (40m) and when the value 400M of used space is reached the plugin stops working despite having gigs of space.
To get it working I delete the 0 byte files, re run, fails... delete a number of the larger backups which are at 63M each (ie about 5-6) and suddenly it works again.
Is there a log file I can check to verify if it thinks it is running out of space..?