I am not completely sure why it passes all the tests. The issue is that there is a cross reference that is not well formed.

1. If the file in the output folder with the .nt extension is opened in a text editor.
2. Select some text that is probably unique from the line above the last line in the file.
3. Open the project in Paratext.
4. Use Ctrl-F to bring up the find box and past in the text selected in step 2.
5. Find in all books.
6. Click on a match to find the location. The next verse likely begins with a cross reference.
7. Edit the cross reference to correct the error.

In the example where this occurred the cross reference was \x * \xo 6:6 \xt 1 \x* (Note that the cross reference text which should be book, chapter and verse is just the number 1.