Running SQL Server DTS Package From ASP.NET Page Problem

I'm having some problems running a DTS package from my ASP.NET appllication. It runs prefectly in debug from my local machine but as soon as I move it to the web server I receive the following error:

Error: -2147467259
Source: Microsoft JET Database Engine
Description: The Microsoft Jet database engine cannot open the file '\serverBPayFilesPay3.xls'. It is already opened exclusively by another user, or you need permission to view its data.

The file is not opened by anyone else and the share permissions are full control for everyone.

My set up is as follows

serverA - Webserver & DB Server
serverB - File Server

The DTS package pulls in the file from serverB to a database table on serverA. The sa account is used for the database connection and connecting to the DTS package from the application. My code for running the DTS package is as follows -

  Private Sub ExecutePackage(ByVal server As String, ByVal package As String, ByVal username As String, ByVal password As String)

Const DTSSQLStgFlag_Default = 0
Const DTSStepExecResult_Failure = 1

Dim oPKG As DTS.Package, oStep As DTS.Step
oPKG = New DTS.Package

Dim sServer As String, sUsername As String, sPassword As String
Dim sPackageName As String, sMessage As String
Dim lErr As Long, sSource As String, sDesc As String

' Set Parameter Values
sServer = server
sUsername = username
sPassword = password
sPackageName = package

' Load Package
oPKG.LoadFromSQLServer(sServer, sUsername, sPassword, _
DTSSQLStgFlag_Default, , , , sPackageName)

' Set Exec on Main Thread
For Each oStep In oPKG.Steps
oStep.ExecuteInMainThread = True
Next

' Execute
oPKG.Execute()

' Get Status and Error Message
For Each oStep In oPKG.Steps
If oStep.ExecutionResult = DTSStepExecResult_Failure Then
oStep.GetExecutionErrorInfo(lErr, sSource, sDesc)
sMessage = sMessage & "Step " & oStep.Name & " Failed<br><br>Error: " & lErr & "<br>Source: " & sSource & "<br>Description: " & sDesc & "<br><br>"
Else
sMessage = sMessage & "Step " & oStep.Name & " Succeeded<br>"
End If
Next

oPKG.UnInitialize()

oStep = Nothing
oPKG = Nothing

' Display Results
'MsgBox(sMessage)

lblOutput.Text = sMessage

End Sub 

I'm using windows authentication with identity impersonate set to true. If I change to use basic authentication and enter my login when I go to the site the DTS package runs successfully. So I assume that I'm seeing this 'double hop' issue.

serverA is for testing so I moved the DTS package and web application to serverB so now everything is on the same server and should eliminate the double hop? No! Works perfectly from my PC in debug, but from the web server the same error occurs. Changing to basic authentication does not workaround the issue on the live server.

The DTS package always works when run from Enterprise manager.

I know this is a premissions issue - does anyone know what I'm doing wrong? Hopefully I've supplied enough info, if not just ask!