Using the Excel Add-In - By Loren Prentice article

I followed the procedure in the article, http://www.mathcad.com/support/item/jan_excel.asp, and discovered than when I changing the a and b values in the Excel worksheet the matrix does not change. I press F9 key and the Recalculate Mathcad Object Button with no updates to the worksheet. If you insert new values for a and b, save and close the file, it will calculate a new matrix when you open the file.
What am I missing?