No matter what you do, right after making any changes and clicking save, get the message below.
and this notification:
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, [no address given] and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.

read more here: https://www.drupal.org/node/440440