Open the rebuilder attached.
Enable macros.
Click the rebuilder tab on the top and far left.
Open the file.
Save.
Just note I didn't make the file, found it somewhere.
:/ should have known there would have been an automated method of doing it.
For the manual method I used, it was something like .docx files are actually zip files.
You rename the file to .zip and extract it.
Note the file and location of the error that the error message gave.
Open up that file in a text editor (an editor designed for XML with a debugger would be best).
Locate the error in the file (as indicated by the error message) and then add in whatever was needed to fix it (I think it was a missing end tag).
Run the debugger to clean up any other errors.
Can't remember what process I used to put it back into a .docx file, I think I had to use some conversion tool for that.