If you receive error messages from Google when trying to open the Google Webmasters Tools integration, ensure that the account used to login to Google is the same account associated with the website domain in Google Webmasters tools and that the domain specified is exactly the same registered in Google Webmasters Tools. The domain must match exactly, so if you have registered http://www.mydomain.com and your are requesting for example http://mydomain.com Google won't allow the access.
In this case you could receive an error message: '(403) User does not have sufficient permission for site 'http://www.sitexyz.com/'
You can set preferred domains for Google Webmasters Tools (and Google Analytics) in the component configuration section as visible below:
Also if you are updating from a previous version of JSitemap and you already have an ongoing login to Google used to access the Google Analytics stats, you must logout and perform a new login. This is required because now the application needs permissions for both Google Webmasters and Google Analytics.
Finally, if you have setup your own Google Application ensure that both API for Google Webmaster and Analytics are enabled in the Google console.
As a side note, after an update from a previous version of JSitemap, it would be ideal clearing the browser cache to have all the panels used in the Google Webmasters dashboard expanded automatically by default.