Unfortunately, a recent update of azure-storage broke duplicity. The fix was not to hard to implement; mostly minor changes in class names, and one simplification in querying blob properties. It took me a few hours to make a fix, and I just submitted my changes as a merge request to duplicity.
UPDATE Unfortunately, I made a mistake and made my changes against the 0.7.14 release rather than trunk. It looks like there is already a lot of work in trunk to deal with the current azure-storage version. So, I withdrew the merge request. I'll work from the 0.8 series branch, instead. Currently, it looks like 0.8 all works as is.