Are you on windows? This is because of permissions on windows are... poor.
To fix this, right click in the same folder that the config file is in, choose properties > permissions. Then click on your name in the list and tick the check box for 'full control'. This will give you ownership of the files so you can edit them properly. Note that you need to be an admin or use an admin password for that.
Hope that works, if not, please post more info.
