OWC11 pivot table export to excel fail: missing tag row (seems to

I am using pivot table of OWC11 in a WPF application(hosted by WindowsFormHost control). But when I click the button to export the table to Excel, I got error like this:

XML ERROR in PivotTable

REASON: Missing Tag

ACTION: Aborting current XML group

FILE: C:\Users\MY_NAME\AppData\Local\Temp\PivotTable71147_cachedata.xml

GROUP: PivotCache

TAG: row

And when I opened PivotTable71147_cachedata.xml file, it looks like this:

<xml xmlns:s='uuid:BDC6E3F0-6DA3-11d1-A2A3-00AA00C14882'...

OWC11 pivot table export to excel fail: missing tag row (seems to