web site administration tool

I'm doing this...

Walkthrough: Creating a Web Site with Membership and User Login (Visual Studio)

with a sqlserver db on my server.

I create this (not mentioned)

< xml version="1.0" >

<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">

<connectionStrings>

<remove name="LocalSqlServer"/>

<add name="LocalSqlServer" connectionString="Data Source=MYSERVER;Integrated Security=SSPI;Initial Catalog=MyDB" providerName="System.Data.SqlClient"/>

</connectionStrings>

<system.web>

<authentication mode="Forms" />

<compilation debug="true"/>

</system.web>

</configuration>

But i can't create user or try login with user created in web site administration tool.

Error:

[SqlException (0x80131904): Impossibile eseguire l'accesso per l'utente '(null)'. Motivo: l'utente non e associato a una connessione SQL Server trusted.]
  System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) +734883
...

Thx.

PS-not say to write on ASP forum because i didn't join it.