If you try to edit the global configuration in Joomla and receive the message
An Error has occurred! Unable to open configuration.php file to write!
On your serverset the permissions for the configuration.php in the root of the website to enable modify permissions to the Internet guest account.
You may also get an error uploading images
Warning: Failed to move file!
Error. Unable to upload file.
Set the internet guest account to have permissions on the following folders and files: