SpreadsheetConverter is a bit picky regarding the arguments to charts. It should be ranges.
This is easy to fix, however, you need to edit the spreadsheet slightly.
When you create charts to be handled by SpreadsheetConverter, it is always best to collect all the data you want shown into a range, mark that range and use the Excel-chart-wizard to create the range. Then, SpreadsheetConverter will be able to convert them.
For chart examples, see