File Name Couldn't Be Downloaded

I am building an excel file using the OpenXml sdk 2.0. I am putting it in a memory stream and outputting it to the browser.The problem I am receiving is wiht IE 9 if I click Open it says "filename couldn't be downloaded". If I hit save/save as and save it to the filesystem, then open it, the file opens fine with no errors.

In Firefox regardless of if I use save or open the file when opened in excel says its corrupt.I already built the file by writing it to the filesystem first and that code works. Also since saving to desktop in IE lets me open the file, im assuming the problem has to be with the settings on the Response.BinaryWrite.

I have tried changing the buffer types, changing the content types to include "application/octet-stream", and tried using the extension/content type for office 2003 instead of 2007/2010...Here is my code

Code:

Dim byteArray As Byte()

Using mStream As New MemoryStream
Using spreadSheetDoc As SpreadsheetDocument = SpreadsheetDocument.Create(mStream, SpreadsheetDocumentType.Workbook)
Dim workBPart As WorkbookPart = spreadSheetDoc.AddWorkbookPart
Dim workSPart As WorksheetPart = workBPart.AddNewPart(Of WorksheetPart)()

[code]...