cant edit content-type settings of custom module

dear list

just wrote my first node module
i implemented all the hooks from the node_example.module ( http://api.drupal.org/api/5/file/developer/examples/node_example.module )
and my module appears in the admin content-type settings ( Home › Administer › Content management › Content types )
now i would like to switch comments and attachments off for my new module-content-type
but i cant ! i get the following error message:
"The human-readable name 'my_module_name' is already taken." ( this is strange because the human-readable name is different then the machine-readable. i set them before in the hook_info() of my module )

well. is there a important hook for editing content-type options which is missing in the node_example.module ?

thanx in advance for any help