It seems to be an issue with the Web.config file or IIS doesn’t have access to the folder where the site is installed. In this case, you should check under which user the Application pool is running in IIS and see if that user has permissions on the folder where the Orchestrator is installed. If the user is “App pool identity” you need to change it with another user.
Please also check the link below and see if any of the solutions there suits you: