Yes. All boolean options are false by default, so supplying them will set them to true, unless the value is either false, no, 0 or off.
The error is a fail-safe check that tests that the database query performs as expected, which is somehow not the case here.
It looks like it is trying to delete the oldest backup and this causes some trouble.
You can try:
sudo mono /usr/lib/duplicati/Duplicati.CommandLine.exe list "ftp://<blah>" --dbpath=/root/.config/Duplicati/BackupName.sqlite
This will show you all the versions Duplicati can find. You can then try to delete the oldest one like this (replace 8 with the right version from the list command):
sudo mono /usr/lib/duplicati/Duplicati.CommandLine.exe delete "ftp://<blah>" --dbpath=/root/.config/Duplicati/BackupName.sqlite 8
Maybe it works better when deleted manually.