Tool to check if XLSX file is valid (according to the specs)

[StefanM]

Hi,

I use a tool (Altova Mapforce) that converts XML data into a XLSX file by
defining a mapping. The mapping can then be applied interactively to a XML
source file or the tool can generate C# code so that the mapping can be
encapsulated and included in other applications. The problem is that the
resulting XLSX files seem to cause problems when being opend in either Excel
2007 or 2003 using the converter.

So that's why I would like to know if there is a tool (other than Excel
itsself) to check if a XLSX file is valid or conforms to the spec.

Thanks,
Stefan