I was getting "Excel found unreadable content" errors in some of my workbooks, but I finally tracked down the issue. To reproduce, start a new workbook and add "NaN" to one of the cells:
Dim wb As New XLWorkbook()
Dim ws As IXLWorksheet = wb.Worksheets.Add("Test")
ws.Cell(1, 1).Value = "NaN"
Upon opening the file, you'll get the "unreadable content" error. If you choose to repair the file, it will then show "NaN" in the cell as expected.
I compared the orignial and repaired versions of xl\SharedStrings.xml, and "NaN" wasn't present in the original file - could that have something to do with it?
Dim wb As New XLWorkbook()
Dim ws As IXLWorksheet = wb.Worksheets.Add("Test")
ws.Cell(1, 1).Value = "NaN"
Upon opening the file, you'll get the "unreadable content" error. If you choose to repair the file, it will then show "NaN" in the cell as expected.
I compared the orignial and repaired versions of xl\SharedStrings.xml, and "NaN" wasn't present in the original file - could that have something to do with it?