What can I do if an error message appears when I access the Cockpit website?

Please try this solution:

After deleting cookies and cache data in Google Chrome browser for the last 24 hours and finally for the last 7 days here in the first step, trying browser restart and even Windows restart, last but not least, please proceed to delete all saved cookies and website data.

Delete cookies and website data in Chrome - Here's how: 

Open the Chrome settings via settings (small cogwheel in the upper right corner). Scroll all the way down and click on the Advanced item. There you will find a field labeled Clear browser data (Clear cache as well as history, Delete cookies and other data) → click on it.

In the next step - at least if you do not want to remove everything across the board - click the Advanced tab. Select Total time, select Cookies and other website data and click Delete data.

This may take a few seconds ...