Keep getting "Login failed for user IIS APPPOOL\DefaultAppPool" no matter what I do

I'm trying to give an ASP NET App access to a database (These are test only not production).

It's the first time I try it in this network, and I haven't done it with VS2012, SQL Server 2012 Express, Windows 7 before

What I have done:

• I upgraded my Sql Server 2012 Express since what VS2012 first installs is a version that doesn't allow access from IIS
• I found that I had to configure SQL Server 2012 Express to accept remote connections, then I followed a good blog I found here
• In SSME 2012, I added a new login for all databases NT AUTHORITY\NETWORKSERVICE (I browsed it and found "Servicio de red" which stands for NETWORKSERVICE, so it is actually NT AUTHORITY\Servicio de red)
• I set dbo as the default schema for this login
• Under login properties, in User Mappings, I checked my Database (which I named MiniNorthwind) and then checked db_datareader and db_datawriter in Database Role Membership for MiniNorthwind
• In Internet Information Services Manager I checked that the DefaultAppPool Identity was ApplicationPoolIdentity (It was the default setting)

But I still get an error saying that Login failed for user IIS APPPOOL\DefaultAppPool, if I change the DefaultAppPool identity to NetworkService, then the error changes to Login failed for user NT AUTHORITY\Servicio de red

I don't know what else to do. Please, need help here.

Rafael

In IIS Manager set DefaultAppPool identity as NetworkService. Although it works, you should try to make it work with AppPoolIdentity, since it the Windows 7 attempt to make it safer