<configuration>
  <connectionStrings>
    <add name="ADService" connectionString="LDAP://mossdc02/, dc=expgroup, dc=ru" />
  </connectionStrings>
    <system.web>
        <membership defaultProvider="AspNetActiveDirectoryMembershipProvider">
          <providers>
            <add name="AspNetActiveDirectoryMembershipProvider"
              type="System.Web.Security.ActiveDirectoryMembershipProvider, 
              System.Web, Version=2.0.3600, Culture=neutral, 
              PublicKeyToken=b03f5f7f11d50a3a"
              connectionStringName="ADService"
              connectionUsername="domain\\userName"
              connectionPassword="password"/>
          </providers>
        </membership>
        <compilation debug="true" targetFramework="4.0"/>
        <httpRuntime/>
        <authentication mode="Windows" />
      </system.web>
</configuration>

protected void Login1_Authenticate(object sender, AuthenticateEventArgs e) {
            string userName = "domain\\userName";
            string password = "password";

            if (Membership.Providers["AspNetActiveDirectoryMembershipProvider"].ValidateUser(userName, password)) {
                e.Authenticated = true;
            }
        }

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: Could not load file or assembly 'System.Web, Version=2.0.3600, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

Source Error:

Line 12: Line 13: type="System.Web.Security.ActiveDirectoryMembershipProvider, Line 15: System.Web, Version=2.0.3600, Culture=neutral, Line 16:
PublicKeyToken=b03f5f7f11d50a3a"