Why does this code cause an error? - asp.net

Question

I have been looking for hours on how to connect to my local SQL database. I can't believe its been this difficult. Anyway, i think I am more on the right track with this code.
<%
Dim myConnection as System.Data.SqlClient.SqlConnection
Dim myCommand as System.Data.SqlClient.SqlCommand
myConnection = New System.Data.SqlClient.SqlConnection("Data Source=localhost;Initial Catalog=dbtest;Integrated Security=True")
myConnection.Open()
%>
However, It still does not work. I don't know where to begin because I also get this message when the page loads:
Runtime Error
Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.
Details: To enable the details of this specific error message to be viewable on remote machines, please create a tag within a "web.config" configuration file located in the root directory of the current web application. This tag should then have its "mode" attribute set to "Off".
I created a web.config file, and it didn't change anything. I'm so lost. Any help is appreciated!
Stack Trace: [SqlException
(0x80131904): Cannot open database
"dbtest" requested by the login. The
login failed. Login failed for user
'IIS APPPOOL\DefaultAppPool'.]
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException
exception, Boolean breakConnection)
+6244425 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject
stateObj) +245
System.Data.SqlClient.TdsParser.Run(RunBehavior
runBehavior, SqlCommand cmdHandler,
SqlDataReader dataStream,
BulkCopySimpleResultSet
bulkCopyHandler, TdsParserStateObject
stateObj) +2811
System.Data.SqlClient.SqlInternalConnectionTds.CompleteLogin(Boolean
enlistOK) +53
System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo
serverInfo, String newPassword,
Boolean ignoreSniOpenTimeout, Int64
timerExpire, SqlConnection
owningObject) +248
System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(String
host, String newPassword, Boolean
redirectedUserInstance, SqlConnection
owningObject, SqlConnectionString
connectionOptions, Int64 timerStart)
+6260362 System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection
owningObject, SqlConnectionString
connectionOptions, String newPassword,
Boolean redirectedUserInstance)
+6260328 System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity
identity, SqlConnectionString
connectionOptions, Object
providerInfo, String newPassword,
SqlConnection owningObject, Boolean
redirectedUserInstance) +354
System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions
options, Object poolGroupProviderInfo,
DbConnectionPool pool, DbConnection
owningConnection) +703
System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection
owningConnection, DbConnectionPool
pool, DbConnectionOptions options) +54
System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection
owningObject) +6261592
System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection
owningObject) +81
System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection
owningObject) +1657
System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection
owningConnection) +88
System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection
outerConnection, DbConnectionFactory
connectionFactory) +6265031
System.Data.SqlClient.SqlConnection.Open()
+258 ASP.index_aspx.__Render__control1(HtmlTextWriter
__w, Control parameterContainer) +71 System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children) +115
System.Web.UI.Page.Render(HtmlTextWriter
writer) +38
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean
includeStagesAfterAsyncPoint) +4240

Answer 1

It's here
Cannot open database "dbtest"
requested by the login. The login
failed. Login failed for user 'IIS
APPPOOL\DefaultAppPool'
The App Pool identity account is set up in SQL Server but is not set up in the database dbtest. You get a different error message if you could not connect to the SQL Server instance, but you are connecting for you to get this error message above.1
So, in SQL:
USE dbtest
GO
CREATE USER [IIS APPPOOL\DefaultAppPool] FROM LOGIN [IIS APPPOOL\DefaultAppPool]
Edit:
When you connect to a "database", you actually authenticate 3 times (basically)
To the Windows/domain install hosting the SQL Server Instance (out of scope here)
To the SQL Server instance, where you are a "login" set up SQL Server via CREATE LOGIN
This login maps to zero or more databases as a "user", which is what you needed to do here
In this case, you were set up in SQL Server as a login but not set up in the target database hosted within the SQL Server instance.

Answer 2

Put the CustomError tag and value properly, like:
<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>
This will expose the exact issue to you.

Answer 3

Try to set Data Source=(local)

Answer 4

Have you followed all the instructions and made sure the customerErrors tag in the web.config looks like this:
<customErrors mode="Off" />
And the real error appears to be that the user ASP.Net is running as does not have permission to log in to the database.