You get the “is read only error” when you have a private property and no getter (e.g. getAuthManager). As far as I know it has nothing to do with if the file is read only or not. Changed the call to Yii::app()->getAuthManager() to avoid using the CComponent’s “magic” get function. Hopefully this resolves the issue.
Also, please make sure that your application configuration is set up as in the installation instructions.
Which version of the framework are you running btw?
Please let me know if this worked for you. Also, please let me know how you like the module. Thank you in advance.