Thanks, I just didn't know how to do this and just figured it out:
1. Log in Google webmastertools,
2. In the menu left go to Api's,
3. In the Api library search for Google Webmaster Tools API,
4. Click on Google Webmaster Tools API just below Name,
5. Enable it.
Thanks for this! I had the same issue, but I could not find API's in the webmaster tools. I ended up finding it in my google developers console, under the project I created for that website - then I went under API's & Auth on the left side, then APIs - in the search box, I put in web, and on the list was the webmaster tools - I clicked on that, then clicked enable. Then, there is one more step - apparently, when you authorize JSiteMapPro for google, it only authorizes what you have at that time - so you have to go into JSiteMapPro and either the Webmaster Tools or Analytics, Logout from Google, then re-authorize. Then it worked fine!