asp.net - error in Webconfig "Server Error in '/' Application" -

i keep getting error in webconfig dunno why. im trying use ad authentication in asp.net c# website

<authentication mode="forms">    <forms name=".adauthcookie" timeout="10"         loginurl="login.aspx" defaulturl="default.aspx"> </forms> </authentication>   <authorization> <deny users="?" /> <allow users="*" /> </authorization>     <membership defaultprovider="domainloginmembershipprovider">   <providers>   <add name="domainloginmembershipprovider"        type="system.web.security.activedirectorymembershipprovider, system.web, version=2.0.0.0,culture=neutral, publickeytoken=b03f5f7f11d50a3a"        connectionstringname="adconnectionstring"        connectionusername="username" connectionpassword="password"/>   </providers> </membership> </configuration> 

your error message self explanatory. can see screen shot have included authentication section directly inside configuration node should present inside system.web node. web.config should this:-

<configuration>     <system.web>       <authentication mode="forms">          <forms name=".adauthcookie" timeout="10"              loginurl="login.aspx" defaulturl="default.aspx">          </forms>       </authentication>  ...others     </system.web>  <connectionstrings>     <add name="connectionstring" .....others </configuration>