Here's a strange problem. We have an application that runs an automated test system. Test parameters are read from the spreadsheet, results are written to the spreadsheet. We perform multiple tests in a run, saving the workbook to the same file at the end of each test (think committing a record to a database). We noticed that after the 2nd test, the spreadsheet becomes empty. There's one worksheet "Sheet1" which has no data at all in it. Should we re-read the spreadsheet after saving it to re-load the object? The object in memory seems to be OK as we continue to grab data from it without problems, we get no exceptions back from the calls to PutValue when we write data from the 2nd test.