PO 7.5 - Operation Mapping error during XSLT

Hello,

I'm facing a problem when testing OM in PO

We have create the XSLT and tested in tools and the transformation is totaly in line with the requirement.

We have uplaoded the xls fil in the Imported archive

We have put the XLS in the OM

And when we are testing we have this error

If we add a line or we delete a line the error is always on the last line with value-of select.

Do you know what is wrong in our configuration.

Thanks in advance for your help.

Jean-Claude