I did a search on the Internet about the problem and couldn't really find anything useful.
You navigate to the Team Sites page and click on the "Site Map" link, you get the following message:
Unable to display this Web Part. The Table of Contents start location, /default.aspx, is unavailable. Check to see if this resource was moved or deleted.
The TOC web part has a default.aspx at the end of the “Start From” location by default and it cannot handle this Url (it needs to be a site Url without a page name). This is how you can fix it (put the page into Edit mode first):
“Open the web part properties and see that the root ("start from") is
indeed set to /default.aspx. Simply change this to / and then the ToC works as