Hi, thanks for the reply!
But the problem I am facing is actually, when I create a new site from the network admin backend, it shows the role of administrator on new created site and new site shown on list of sites in network admin below the site's registrar's name. That is ok.
But when a new user registers by sign up form and get a new site, problem is here. Here I can see the "administrator" role only on new created site, in network admin's site list, I can see the site name and all details but below the new site registered user, it shows "()", which is not able to identify the role of new registered user in multisite network.
This is the reason, when we use Pro Sites plugin from WPMU, which need administrator role to upgrade, not working with front end registration process but it is working well when I create a new site from backend.
I deactivated all the plugins used in my multisite for testing the registeration process if it was not effected by any plugin. But it was not showing the assigned role on network admin's site list, so I concluded that it must be a cause with main core wordpress functionality. And if it is, then I must need to replace the concern file which handle the role identification functionality or reinstall the core wordpress software. But I am afraid, that it may destroy all other plugin settings or content on site??
so here is the main issue mentioned, please suggest. Thanks!!