If you see this error when you try to enter your website properties via your control panel, it might have to do with your web.config file under the wwwroot directory. The following artical will show you how to use your File Manger from your control panel, to rename it to web.config.old and re-create a new web.config file.
To fix the issue you need to rename the web.config file.
1) Click on File Manager
2) Click on your domains directory
3) Click on wwwroot
4) Click on the rename icon beside the web.config file
5)Type a new name for it (web.config.old),and click Rename
6) You will see the file renamed
7) We now need to generate a new web.config file,click on Websites
8)Click on your Website name
9)Click on Update
10) It will now show you that it is updating
11)Your website should now be working again, the main thing to consider is, that the control panel and your website are sensitive to changes made in your web.config file, so unless you know exactly what you are doing, do not alter the original web.config file’s content. Only add to it, but don’t change settings that were automatically and originally created by the control panel itself. Doing this wrong, will break your control panel again, and cause your website to not work, again.