Authentication and Authorization of Users In Active Directory and Application Roles (SQL)

Question

My application is composed of users located in three Active Diretory groups, TIRES Users, TIRES Super, TIRES Admin.  Using the following code I can determine which of the three groups a user to the application is assigned to.
Dim strAdmin As String
strAdmin = " TIRES Admin"

If (Roles.IsUserInRole(strAdmin)) Then
'continue
Else
Response.Redirect(http://tires/home.asp)
End If

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The next step I undertook was to create three SQL Application Roles, TIREAdminCRUD, TIRESuperRU, TIRESUser.
Each group were given execute right to various stored procedures with the schema as 'dbo'.

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How now do I, in the Page_Load Event, utilizing Roles.IsUserInRole(strAdmin)) , determine which SQL Application Roles the user belongs to in order to have the right user execute or not execute the correct stored procedure?

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My web.config connection string is:
<add name="TIREConnectionString" connectionString="Data Source=DOMAIN\INSTANCE;Initial Catalog=Tires;Integrated Security=True"/>
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When I attempt to view the web page on our Intranet I receive the following error message:
Login failed for user 'DOMAIN\SERVER_NUMBER$'.
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I have read at least a dozen various web web sites over the past two weeks, at least, and tried many diffect scenaios to no avail! 

Specifically, what do I type to get this working and where? 

Thank you, greatly!!

Ayomide