Possible reasons:
1. Check that your component interface is included in a permission list that you have access to. Also check that you have access to all possible methods (Get, Save, Create, Cancel, Find). If you delete a component interface through application designer, it is also removed from any associated permission lists so this may be another reason why your new component interface (with the same name) is not authorized any more.
2. Make sure you are not trying to do something in your code that the CI can't do. For example, if your CI doesn't have a create method, you can't set security for it, so you will get a not authorized error if you have code that attempts to perform a create. This is because the authorization error is usually the first error to be displayed.