I'm writing data out to an Excel file. When I save I get "Exception from HRESULT: 0x800A03EC" on the save line below

oSheet.SaveAs(ExportParams.sResultFileName, 
                            Excel.XlFileFormat.xlWorkbookNormal,"", "",false, false, false, null,null);

The params appear to be correct according to the object browser and this http://msdn.microsoft.com/en-us/library/microsoft.office.tools.excel.worksheet.saveas(VS.80).aspx

I could use some help.