Under certain circumstances the DocViewSaxFormatter does not emit any namespace declarations. That is the case for an aggregate not having any namespaced properties (e.g. due to lack of read privileges) and not having any namespaced child elements. The generated .content.xml then looks like this:
This XML is invalid and leads to exceptions during import.
The problem is that the namespace for jcr is always necessary as the root element is always named jcr:root.