I would really recommend using duplicity[1]. It supports gpg, incremental backups and more.
Anyway, I would recommend against using it - errors like that should be impossible when you're not doing anything exotic.
> Although you should never have to look at a duplicity archive manually, if the need should arise they can be produced and processed using GnuPG, rdiff, and tar.
I haven't set it up yet, but it's going to be my holiday project this Christmas..