Describes the cause and action for error messages.
Error Message(English)：
error unreadable content
PhpExcel error - Unreadable content when opening in Excel - Stack ...
https://stackoverflow.com/questions/10194431/phpexcel-error-unreadable-content-when-opening-in-excel・・・
Excel VBA 2010: Data validation breaks when workbook ...
https://stackoverflow.com/questions/53611926/excel-vba-2010-data-validation-breaks-when-workbook-sav・・・
JasperReports xlsx export error - Unreadable content - why ...
https://stackoverflow.com/questions/15024396/jasperreports-xlsx-export-error-unreadable-content-why
OpenXml DataValidation set predefined List for columns
https://stackoverflow.com/questions/33886205/openxml-datavalidation-set-predefined-list-for-columns
Unreadable Content Error | PC Review
https://www.pcreview.co.uk/threads/unreadable-content-error.3894486/
54591 ? Excel: unreadable content error when opening POI generated ...
https://bz.apache.org/bugzilla/show_bug.cgi?id=54591
55800 ? cloneStyleFrom(CellStyle cellStyle) creates error ...
https://bz.apache.org/bugzilla/show_bug.cgi?id=55800
XML
https://bz.apache.org/bugzilla/show_bug.cgi?ctype=xml&id=55800
Mastering cell validation lists in Excel - sverrirs.blog
https://blog.sverrirs.com/2017/03/excel-cell-validatelist-in-vba.html