Forms Data Controls :: Saving Repeater Data As .xlsx File?

Using the Interop for Excel 2003 I had a nice little link that saved or opened the repeater content as .xls. Now we are using Excel 2007 and I get file format error messages. When I click the OK button on the error pop-up Excel closes. Does anyone out there know how to convert my code to handle the .xlsx format? I've been reading up on Interop for 2007 but none of the examples seem to work for this particular simple task. Here is my code from the "Export to Excel" button click:

Protected Sub btnExport_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnExport.Click
' Send HTTP headers that specify Excel filename, MIME type, and character set
Dim sTemp As String = "attachment;filename=CoverageCase" & Session("OpenCase").casekey.ToString & ".xlsx"
Response.AddHeader("content-disposition", sTemp)
Response.ContentType = "application/vnd.ms-excel"
Response.Charset = ""
' Create objects used to render the controls
Dim strw As New System.IO.StringWriter........

I found a thread from a couple of years ago dealing with this but there was no solution [URL]. There were a couple of tortureous work arounds but neither work for me.