Calling from Access To Stored Procedure that Use Linked Server - sql-server-2008

Question

I have Access that is used as Front End (UI) for the users, let's call it Acc1.
Acc1, is linked to tables on SQL Server.
From Acc1 I want to call to Stored Procedure, let's call it SP1.
SP1, is a simple select on a table in Linked Server. The Linked Server is an Access DB that has only tables. Let's call this DB Acc2.
Note: In the future SP1 will query more complex query that will use table from the Acc2 and from the SQL Server database. Right now as first step I want to execute this simple select query.
When I do in SP1 a simple Select query on a table from the SQL Server table, and try to cal it from Acc1, that's work.
When I try to query the linked server table in SP1 and try to call it from Acc1 it fails with error:
When I run this SP1 from SQL Server it is working.
Any ideas why it happened? How can I do it?
Following is the code:
The SP1:
ALTER PROC [dbo].[spSpanDates_BMPWorkFlowSpanCounts]
AS
BEGIN
SELECT *
FROM
[Supplemental_Form_master_tables]...[tblBPMWorkflows]
END
The code in Acc1:
Private Sub Button_BPMStartEndDatesALL_Click()
Dim qdf As DAO.QueryDef, rst As DAO.Recordset
Dim FindRecordCount As Long
Set qdf = CurrentDb.CreateQueryDef("")
qdf.Connect = "ODBC;DRIVER={sql server};DATABASE=PLMScheduling; SERVER=USCLES425\INST2; Trusted_Connection=Yes;"
qdf.sql = "EXEC dbo.spSpanDates_BMPWorkFlowSpanCounts"
qdf.ReturnsRecords = True
Set rst = qdf.OpenRecordset(dbOpenSnapshot)
If rst.EOF Then
FindRecordCount = 0
Else
rst.MoveLast
FindRecordCount = rst.RecordCount
End If
rst.Close
Set rst = Nothing
Set qdf = Nothing
End Sub
I'm using SQL Server 2008 and Access 2010.
Thank you very much for the help!

Answer 1

The answer is very simple. When SP1 run from Acc1, SQL Server uses the permissions of Acc1. So when try to query in SP1 tables from Acc2 with the permissions of Acc1 this fail.