I have searched through every possible answer on SO for a solution, but nothing has worked. I am basically creating an excel file from a database and sending the results to the response stream using EPPlus(OpenXML). The following code gives me an error when trying to open my generated excel sheet "[report].xlsx is locked for editing by 'another user'." It will open fine the first time, but the second time it's locked.

    Dim columnData As New List(Of Integer)
    Dim rowHeaders As New List(Of String)
    Dim letter As String = "B"
    Dim x As Integer = 0
    Dim trendBy = context.Session("TRENDBY").ToString()

    Dim dateHeaders As New List(Of String)
    dateHeaders = DirectCast(context.Session("DATEHEADERS"), List(Of String))
    Dim DS As New DataSet
    DS = DirectCast(context.Session("DS"), DataSet)

    Using excelPackage As New OfficeOpenXml.ExcelPackage

        Dim excelWorksheet = excelPackage.Workbook.Worksheets.Add("Report")

        'Add title to the top
        With excelWorksheet.Cells("B1")
            .Value = "Account Totals by " + If(trendBy = "Months", "Month", "Week")
            .Style.Font.Bold = True
        End With

        'add date headers
        x = 2 'start with letter B (aka 2)
        For Each Header As String In dateHeaders
            With excelWorksheet.Cells(letter + "2")
                .Value = Header
                .Style.HorizontalAlignment = OfficeOpenXml.Style.ExcelHorizontalAlignment.Right
                .AutoFitColumns()
            End With
            x = x + 1
            letter = Helper.GetColumnIndexToColumnLetter(x)
        Next

        'Adds the descriptive row headings down the left side of excel sheet
        x = 0
        For Each DC As DataColumn In DS.Tables(0).Columns
            If (x < DS.Tables(0).Columns.Count) Then
                rowHeaders.Add(DC.ColumnName)
            End If
        Next
        Dim range = excelWorksheet.Cells("A3:A30")
        range.LoadFromCollection(rowHeaders)

        'Add the meat and potatoes of report
        x = 2
        For Each dTable As DataTable In DS.Tables
            columnData.Clear()
            For Each DR As DataRow In dTable.Rows
                For Each item As Object In DR.ItemArray
                    columnData.Add(item)
                Next
            Next

            letter = Helper.GetColumnIndexToColumnLetter(x)

            excelWorksheet.Cells(letter + "3").LoadFromCollection(columnData)

            With excelWorksheet.Cells(letter + "3")
                .Formula = "=SUM(" + letter + "4:" + letter + "6)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "7")
                .Formula = "=SUM(" + letter + "8:" + letter + "11)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "12")
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "13")
                .Formula = "=SUM(" + letter + "14:" + letter + "20)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "21")
                .Formula = "=SUM(" + letter + "22:" + letter + "23)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "24")
                .Formula = "=SUM(" + letter + "25:" + letter + "26)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "27")
                .Formula = "=SUM(" + letter + "28:" + letter + "29)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            With excelWorksheet.Cells(letter + "30")
                .Formula = "=SUM(" + letter + "3," + letter + "7," + letter + "12," + letter + "13," + letter + "21," + letter + "24," + letter + "27)"
                .Style.Font.Bold = True
                .Style.Font.Size = 12
            End With

            x = x + 1
        Next

        range.AutoFitColumns()

        'send it to response
        Using stream As New MemoryStream(excelPackage.GetAsByteArray())
            context.Response.Clear()
            context.Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
            context.Response.AddHeader("content-disposition", "attachment;  filename=filetest.xlsx")
            context.Response.OutputStream.Write(stream.ToArray(), 0, stream.ToArray().Length)
            context.Response.Flush()
            context.Response.Close()
        End Using
    End Using