Full message:
LibreOffice 5.1.2.2
Error saving the document Untitled1:
Write Error.
Error in writing sub-document styles.xml.
After I did modified the style a little, I tried again and got the same message but with “content.xml”.
Another attempt got me a “General input/output error”.
I copied and pasted my entire document into Google Docs, then copied and pasted it back and still got the “content.xml” error.
Next, I tried copying a little at a time from Google Docs, and this sometimes worked, but sometimes I’d get the content error, sometimes one about $(ARG1).
I downloaded 5.1.2.4 and I was able to save for a while; but now I can’t save again. 
I downloaded 5.2.0, same thing.
There’s nothing wrong with the file, because I sent it as an email attachment to another computer, and I could save it from LibreOffice with no problem.
Same error here: Error in writing sub-document styles.xml (MacOS 10.12.6, LO 5.4.1.2), running on MacBook Air).
Tried most (all?) the suggestions that were posted in 2013, no joy.
So, this morning I thought about saving it as a different file type, OTHER than .odt
Lo-and-behold, .doc saved with no issue, so I guess I’m going to use this file type…
I guess that there’s nothing wrong with the file itself, and everything to do with something LO is doing (or not).
Anyone else has any better idea(s)?