What to do for my application to can create sites on IIS7?

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IIS7

IIS

MVC4

I am working first time with IIS. I made an asp.net-mvc-4 application which have to create a new web site. All worked fine on the server until I installed Microsoft.Web.Administration class library. Server gave me this error:"The Role Manager feature has not been enabled." After I made these changes in web.config:

<pre>
     <appSettings>
<add key="enableSimpleMembership" value="true" />...

 <system.web>
<identity impersonate="true"/>

...

my code:

    ServerManager serverManager = new ServerManager();
Site mySite = serverManager.Sites.Add(websiteName, sitePath, 80);
mySite.ServerAutoStart = true;
serverManager.CommitChanges();

Libray "Microsoft.Web.Administration" is in aplication on server. I tried to change Application Pool Identity with no luck. Now, when I try to create site, redirect on the login page. Please help me, if anyone now how to solve this problem. Thanks in advance!