[web2py] Problem opening downloaded excel sheet using IE

[Jim S]

 I have the following code that generates an excel spreadsheet and then 
downloads it to the user workstation: 

from reports import movementDetail as rpt
letters_file = StringIO.StringIO()
returnVal = rpt.process(originationId, fromDate, toDate, filter,letters_file
, auth.user.id)
 
if returnVal:
    excelFile = letters_file.getvalue()
    letters_file.close()
    response.headers['Content-Type']='application/vnd.ms-excel'
    return(excelFile)




Works fine with Firefox, Opera and Chrome.  When test this with IE, the 
browser login window pops up.  I can cancel the login window and then the 
sheet opens up, but don't know why it is doing that in IE only.  Any ideas?

-Jim

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