The first error you reported is the real one [1]: "Operation not supported by backend." Samba has a history of being a bit flaky over gvfs. I'll try to reproduce here and see if I know why this is happening for ya.
[1] Don't bother running deja-dup with sudo, it's not surprising that it doesn't work. Root doesn't have the same access to the user's DBus session that the user does. So a lot of stuff (including all gvfs file operations) fails.
Thanks for the update, Wolf!
The first error you reported is the real one [1]: "Operation not supported by backend." Samba has a history of being a bit flaky over gvfs. I'll try to reproduce here and see if I know why this is happening for ya.
[1] Don't bother running deja-dup with sudo, it's not surprising that it doesn't work. Root doesn't have the same access to the user's DBus session that the user does. So a lot of stuff (including all gvfs file operations) fails.