If Smart View and Spreadsheet Add-in are installed on the same computer, HVE Workbook (.twb) files are opened in Windows Explorer by Smart View even if the file was created in Spreadsheet Add-in.
If you uninstall Smart View and retain Spreadsheet Add-in on the computer, the file association for .TWB files is lost. Use Windows Explorer to establish .TWB file association manually with Spreadsheet Add-in.