Blank page showed after Snapshot Pro nearly done a backup

I have recently signup a trail member and cant wait to try out some cool plugin from WPMU.
I have some questions after trying Snapshot Pro.

1) is that normal that page went blank (white) when a backup done/ nearly done. I have check the backup file via FTP and saw some temp file and a zip file, i assume the backup not done? i tried few times and always come to this at the end

3) there is a schedule option for each snapshot, if next snapshot run, will it run it from he begining or check from the last change and backup the latest data only? if it will rerun completely, will it rewrite the backup file? and if the second run fail, we lost the old backup file as well?