The underlying provider failed to open , login failed for user IIS APPPOOL

Question

i am not a sql server guy but i am working on a client's application and want to connect to the database through EF Code first

the Exception message that i have is

The underlying provider failed to open

The Exception details

Cannot open database [DatabaseName] requested by the login. the login failed

login failed for user 'IIS APPPOOL\ASP.NET v4.0"

My web config

<add name="TraininGoDB"
    providerName="System.Data.SqlClient"
    connectionString="Server=LOCALPCNAME\SQLEXPRESS;Database=[DATABASENAME];Integrated Security=True;"/>

The EF context and entities are defined in a separate project with the app config of the following

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=4.3.1.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
  </configSections>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="Data Source=(localdb)\v11.0; Integrated Security=True; MultipleActiveResultSets=True" />
      </parameters>
    </defaultConnectionFactory>
  </entityFramework>
</configuration>

i am using SQL Server Express 2008

don't know the problem from the database configration or from the web config

Solution

The user under which the web application pool (associated to your web application) is running doesn't have permissions to access your database. You need to grant it permissions or run under another user who has permissions. So, to summarize: check under which user your application pool is running, then check that that user has access to your database.