Hello Sadaf,
User roles are merely sets of permission configurations (to pages, microflows, entities, etc...). In order to log in, you need a user to be created (a user is created by creating an object of an entity System.User or an object of an entity that is a specialization of the entity System.User… Check the administration module for a ready-to-use setup for doing just that) and then that user object needs to be linked (through the association UserRoles) to the user roles this user is supposed to get.
As for the error you are getting, I’m not sure what you’re trying to access. Sorry.