"I was updating my Table of Contents..."
What specifically were you doing to update the ToC?
"I added a new page and its page number. The problem is that when I add this new entry,..."
You added a new page to the document, or to the ToC? Manually changing the ToC won't work because the ToC doesn't actually exist. It is just a field code that Word uses to generate a ToC when the fields are refreshed.
