Error message switching between docx and odt

I was working on a docx for someone in odt and sent it back then we couldn’t open it. The error read: File format error found at
SAXParseException: '[word/document.xml line 2]: Attribute w:cstheme redefined
', Stream ‘word/document.xml’, Line 2, Column 1900(row,col).

Please help! I looked for a solution but it said to go back to an old version (4) of Libre Office. When I looked into doing that, it said that I had to uninstall version 5 first. Won’t I lose my documents? Is there another alternative?

Another alternative is upgrading to current version - 6.2 or 6.3.

Won’t I lose my documents?

The finished product (your document) is an independent entity which exists regardless of the state of the tool (LibreOffice). Just like when you whittled your mom’s favorite rolling pin beyond recognition. Throwing away the knife would not unwhittle what was whittled. In other words. You will not lose your documents by uninstalling the office suite. You will temporarily lose the means to sensibly access them, but that is rectified by installing a version of the suite again.

What else to do?

The better alternative is to heed Mike’s advice (see comment to your question) and install a current version. That way you won’t need to uninstall anything first. Current versions do not have the bug that would sometimes render files unreadable, so this takes care of future documents you save. It may not help with the current troublesome document if you only have that in docx format.

There have been multiple questions in the Apache OpenOffice forum dealing with this kind of problem, and I understand that a good part of the troubled documents can be salvaged. You may want to go there if you still can’t open your file, and you don’t get immediate help here. I don’t know the format specifics well enough, so can’t help you out of that pickle. Sorry!

See Mike’s comment below, which lists solutions and explanations in this site. Not sure why my SAXparse search didn’t turn up anything. I must have mistyped something.

Also see Which version of LibreOffice fixed the SAXParseException error?

and generally