Don't make those files read only. Dreamweaver needs to be able to update files in the _mmServerScripts folder.
Can you paste this into your browser: http://127.0.0.1/registration_tutorial/_mmServerScripts/MMHTPPDB.php and have it not show a 404 error.
Does that path look correct to you? Usually this problem is a bad url in the testing server section of your Dreamweaver site definition.