Run-time error '3112' Record(s) cannot be read; no read permission

I have an Access 2003 FE & BE database running on a PC. The source for a 
Combo box is a simple query that selects all 6 fields from a Sales Source 
linked table. I have an After Update Event which checks the OldValue from
the 
Combo Box to see if it is a particular type of sales source, as it uses
the 
information to update counters. 
When a user selects a different value in the Combo Box and so triggers off

the After Update event, I get the 3112 error on the OpenRecordset
statement. 
Can anyone offer advice, please? Is there a conflict between the query and

the statement?
 
Coding in the after-update event calls a function that contains the 
following: 

Function GetSalesSource(SalesSourceId As Long) As String

    Dim db2 As DAO.Database
    Dim rst2 As DAO.Recordset
    Dim pathname2 As String
    Dim dblocation2 As String
        
    pathname2 = Application.CurrentProject.Path
    dblocation2 = pathname2 & "\Tables\system tables.mdb"
           
    GetSalesSource = "N"
    Set db2 = OpenDatabase(dblocation2)
    Set rst2 = db2.OpenRecordset("Sales Source")
    
    rst2.Index = "SSrc_Id"
    rst2.Seek "=", SalesSourceId
    If rst2!SSrc_Description = "Repair Only" Then
        GetSalesSource = "Y"
    End If
    
    rst2.Close
    db2.Close
   
        
End Function