Why does Inserting a Table of Contents not work in Version 4.2.5?

I have used the Inset Table of Contents operation in previous versions of LibreOffice, but it does not work in the most recent version.
How can I get it to work?

It does work - at least in one test incident (LO 4.2.5, Win 7 -64). You are going to have to be more specific about your situation, eg operating system and version, exactly what you tried to do and how you tried to do it, what results or error messages you did get (if any), characteristics of the problem file and, if possible, a small reproducible example. For example, have you had this issue on multiple files or just one? What are the characteristics of the problem file? Did you create it or was it from someone else? Was it created in LO or another application? What file format? Are heading and paragraph styles properly defined? If you get the heading “Table of Contents” but nothing else, it is most likely because heading styles have not been properly defined. It amazes me how many people manually format each and every heading etc rather than simply applying styles. Also, in the insert Table of Contents dialogue, check which checkboxes are ticked, particularly “Create from… Outline”.

Try a very simple test case:
Create a new document.
Type “Heading 1” and assign it heading 1 style.
Type “Heading 2” and assign it heading 2 style.
Anywhere else on the page insert a Table of Contents.

Thanks for the explanation and direction; I just joined LO Help because of this issue, with two different documents I created in LO. Assigned heading 1 to all chapter headings, but will not populate below the Table of Conents header, which does populate when I create the TOC. I tried it in both Doc and Docx files. Will try what you mentioned iwth heading styles to see if that helps!

No. It does not work in the latest version. I have done exactly what you describe and, in the previous version, it worked perfectly - and still does on my laptop. What has changed in LibreOffice 4.2 from 4.1 that has changed so that this operation does not now work?
I have done all the checks you mention and the table does not generate, apart from giving the Heading “Table of Contents”

My point was that it is working fine in the latest version for many of us, though obviously not in your specific case. As you have checked the more obvious settings, etc, you might like to submit a bug report.