Spreadsheet_Excel_Writer row limitation?

I'm trying out Spreadsheet_Excel_Writer and it seems to work as advertised -- I'm pretty impressed. However I'm having one major problem, which is that files with a large number of rows cannot be opened by Excel. I get an error that says "The file may be read-only, or you may be trying to access a read-only location." This happens whenever I create a worksheet with more than about 3000 rows. If I stay below that, everything works fine. I'm wondering if this is a bug, since Excel is supposed to support 65536 rows per workbook. thanks, -josh