Mac OS 10.11.5
The DDR XLM can be invalid when certain character are not encoded (and thus fails to load in BaseElements for example).
Two examples I can give:
1. CustomStyle name contains a "&" character.
2. A graph label contains funny characters (eg: "T Y Tota;" did the trick)
There are probably many more examples of unencoded text which could break the xml. Please encode them all.