! Deleting a chart serie resulted in an exception.
! Adding chart series could result in an error message when the file was opened in excel.
! When reading a non existent file, there was no default worksheet, and accessing cells resulted in an exception.
! Adding formulas with percent operator resulted in an exception.
! When exporting to HTML, background colors where wrong.
! The property PrintSettings.StartingPage didn't work.
! Memory leak when deleting rows.