Comment 1 for bug 531178

The 0.4 series is out of date by years. While I can't find anything in the docs that indicate it should not be restorable by the 0.6 series, I suspect enough changes have been made regarding error checks that older versions may be violating something that the new code requires. You can still download the old version from:

http://download.savannah.gnu.org/releases-noredirect/duplicity/OLD/