Thanks wp, I appreciate your quick and clear reply. I follow the logic, and the work around.
It seems to me that for automatic detection the file extension 'ods' should be considered in addition to the fact that it is a 'zip' file, since it fails otherwise.
I will either ignore the exception or code it to use the format specifier sfOpenDocument for 'ods' files, probably the latter.
Again, I appreciate the continued work on FPSpreadsheet it is impressive, and I have not even delved into the visual components yet.