How get Drupal Alias from given node NID inside a module function?
It looks like you are debugging through watch dog table, you should better use devel module it provides you several debugging options few are


dpm()
example in your case : dpm(drupal_get_normal_path('node/866'));
devel/php path
which allows you to test your php codes.
example in your case : simply log in as admin visit sitename/devel/php and execute  dpm(drupal_get_normal_path('node/866')); and see what it shows


About the problem


Make sure node/866 exists
If node exists make sure when you are able to access the node-866 by node/866 and alias which you have configured.
As as an option you can delete the existing alias and create the same alias again. And check again.