Invalid XML when generating Word document for Reporting module


I’ve created a document template in Word (docx), and uploaded it as a template to my Cuba application. When I generate a report based on this template in PDF, everything works fine.

When I want to generate a the report with docx as output format, I have errors opening the document in Word. Word 2016 tells me that there’s errors opening the document.

The details of the error (translated to english) are

The XML data is invalid according to the schema
Location: Part: /word/document.xml. Row 0, Column 0

Any idea what could be wrong or where to look?

I did some further investigation, and I even get this error when I use an empty .docx document as a Word template.
I’m using Cuba 6.6.1

Is there anything that needs to be done to make this work? Is there any dependancy of OpenOffice / LibreOffice?

Could you share the report?
You can export it in Zip on the Reports->Reports screen.