I did that. Its not about the permissions, its about the reports of all extensions. When you login as a particular user, you can only view the reports related to the extension associated with your login only. I cant find any options to enable the user to view reports of all extensions.
What I had to do was delete all extensions, then create the users, and since there are no extensions present in the system it allows to create the user without associating any extension with the user. And then create the extensions. This way when you check the reports you can view reports of all extensions. But the catch is once you want to edit the password or the name, you will definitely have to associate the user with an extension from the drop down menu since its compulsory.
Hope someone can figure this out.