In a Tagged PDF —
While TH and TD may both be a child to TR (cells in a table row) it is not permitted to have a TH as a child of a TD (a cell within a cell that is part of a row).
Nor is it permitted to have a TD as a child of a TH (again, a cell within a cell that is part of a row).
When either is present the error "Table Header (the TH) or Table Data (the TD) is not a child of TR" is presented via Full Checker.

From the screen capture  -
I suspect the first row may be contributing to the problem
That row (containing "Record of Updates") should be a "repeat..." row selection back in Word.
In the PDF you must also set the Column Span to a value of "8".
The second row is also a header row. In the PDF remember to set each cell as a "Header cell" having a Scope of "Column".
Because the table shown has two vertical groups of "header columns" you've a problem.
If you carefully set the required Headers attribute for each table cell and the requisite ID entries for all cells a table with a single column (preferred is the first column only) holding TH cells one can get to a reasonably accessible PDF.
The screen capture shows a table with the first and the fifth columns have cells intended to serve as TH cells.
As providing proper Headers attributes and ID entries is entirely a manual operation getting the screen capture table set up correctly will be a non-trivial endeavor.
It can be done but there's still a problem.
None of the typically used AT applications (NVDA, Windows Eyes, JAWS) deal effectively with such tables.
In part this is due to ISO 32000-1 (the PDF Standard) not identifying a normative algorithm for implementers to associate headers with row and column TH cells' ID entries.
Fortunately this will be addressed in ISO 32000-2.

Having a copy of ISO 32000-1 on hand can be most helpful.
An ISO authorized copy is available from Adobe.
Adobe's ISO 32000-1
http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/p df/pdfs/PDF32000_2008.pdf 

Section 14..8.4.3.4 Table Elements and Section 14..5.7 Table Attributes are key to understanding Tagged PDF's Table element/tag and the allowed child elements/tags..

Back to the possible source of the issue(s).
I'm thinking something is awry back in the Word authoring file.
I'd have to have a file for a look-see to be sure.

Something I'd do. Get "Record of Updates" out of the first row; dump that row.
Have "Record of Updates" as, perhaps a Word Heading 3 ("Section 1 ..." as a Word Heading 1 and "Overview" as a Word Heading 2).
Of course one would use Word's built-in Headings as with PDFMaker's tag management assures proper role mapping of these to PDF's Heading elements/tags.
The idea is to have "Record of Updates" be a table caption.
Unfortunately Word does not appear to have a built-in "table caption/title" still that could be programmatically role mapped to the "Caption" element/tag.
Just have the No. , Date, ... header row.
Have only one "No." column.
First row is your "header row" and all cells are "TH".
All subsequent rows are "data rows" and all cells are "TD".

Be well...