Thank you for posting the file.
The problem is that OpenXML seems to write xlsx files in a different way than Excel does. The worksheet list - which causes the crash - is written by Excel (and fpspreadsheet) like this:
<sheets>
<sheet name="Sheet 1" sheetId="2" r:id="rId1" />
</sheets>
But your file uses here a namespace "x":
<x:sheets>
<x:sheet name="Sheet 1" sheetId="2" r:id="rId2" />
</x:sheets>
And it is not only the sheets node - almost all nodes are in namespace x, and this means changes at numerous places --> Fixed in r6726.