Format Error - headers inserting into the document automatically in the wrong places

Are you talking about the Page Header or a Heading paragraph?

Can you provide a screen shot of the issue.

Word can not have more than one real header on a page. As Doug posted, can you share a screen shot? Could it be a textbox on the page?

It is interesting that you mention that you can see the "additional headers" in outline view. Normally in outline view you do NOT see headers at all.

Sorry I am referring to paragraph headings. I fixed the text in outline view hoping that the problem does not come back. So I cannot send a screen shot.

I tried 2 solutions. Firstly I tried changing the style of the affected paragraphs to Normal style (Home Tab, Styles Section). This appeared to work as this was removing the non-heading text from the TOC. However when I had worked with this file in Word 2007 then back to Word 2010 the problem came back.

The second thing I tried was going into Outline view selecting the affected paragraphs and changing them to body text in the Outline tools section.

So far this seems to be working.

It is possible that this document is automatically updating the styles when you open it and this is importing a dodgy style from its attached template on one of your machines.

Go to the Developer Tab and click the Document Template button. Is the "Automatically update document styles" checkbox ticked?

I tried 2 solutions. Firstly I tried changing the style of the affected paragraphs to Normal style (Home Tab, Styles Section). This appeared to work as this was removing the non-heading text from the TOC. However when I had worked with this file in Word 2007 then back to Word 2010 the problem came back.

That would seem to suggest either that one of the Word installations is faulty or that the document has some form of corruption.

I suggest repairing both Office installation (via Programs & Features > Microsoft Office > Change in the Windows Control Panel).

As for the possible document corruption, documents can often be 'repaired' by inserting a new, empty, paragraph at the very end, copying everything except that new paragraph to a new document based on the same template, closing the old document and saving the new one over it. Similarly, corrupt tables can often be 'repaired' by converting the tables to text and back again or by saving the document in RTF format, closing the document then re-opening it and re-saving in the doc(x) format.