<add name="SiteSqlServer" connectionString="Data Source=.\SQLExpress;AttachDbFilename=|DataDirectory|Database.mdf;Integrated Security=True;User Instance=True" providerName="System.Data.SqlClient" />

it worked until i rebooted the server and i had made no changes to the file...i am using apppoolidentity...this makes no sense



but there is more information:

Log Name:      Application

Source:        MSSQL$SQLEXPRESS

Date:          6/3/2011 7:55:38 PM

Event ID:      15369

Task Category: Logon

Level:         Error

Keywords:      Classic

User:          IIS APPPOOL\websitename

Computer:     

Description:

Failed to generate a user instance of SQL Server due to a failure in impersonating the client. The connection will be closed. [CLIENT: <local machine>]

Event Xml:

<Event xmlns="http://schemas.microsoft.com/win/2004...">

  <System>

    <Provider Name="MSSQL$SQLEXPRESS" />

    <EventID Qualifiers="49152">15369</EventID>

    <Level>2</Level>

    <Task>4</Task>

    <Keywords>0x80000000000000</Keywords>

    <TimeCreated SystemTime="2011-06-03T23:55:38.000000000Z" />

    <EventRecordID>2148</EventRecordID>

    <Channel>Application</Channel>

    <Computer></Computer>

    <Security UserID="removed" />

  </System>

  <EventData>

    <Data> [CLIENT: &lt;local machine&gt;]</Data>

    <Binary>removed</Binary>

  </EventData>

</Event>