Why are the name of the days not shown in my spread sheet?

I’m using an existing spreadsheet for our timesheet record in office. Using microsoft office works fine, but using libre will show 502 error. Attached is a sample. any idea how to fix this? Sample file

I am also seeing the #VALUE! error in the cells in MS Excel 2016 (US English UI on Russian OS); it cannot give the result of DATEVALUE(“1/Oct/2018”). Strings like that are, naturally, a nightmare, not dates. The only date format that doesn’t depend on locale settings and all peculiarities is the ISO “yyyy-mm-dd” format, which requires numeric month. Then, you’d not need the DATEVALUE in that case (slower), when you could use DATE(YYYY;MM;DD) if you had all the numbers.

Whether text can be interpreted as a date value highly depends on the locale worked in. “1/Oct/2018” is not a valid date format in en-US, where the date order is M/D/Y. Excel may be more lenient in what strings it accepts as dates, Calc is a bit more strict (though given there are two numbers with the second being 4 digits and one month name maybe could accept this as well). Working in an en-US locale any of “Oct/1/2018” or “1-Oct-2018” or “2018-Oct-1” would be accepted. Any non-English locale (where month names differ) would cease to work anyway.

To be locale (and application) independent the only safe bet is the ISO 8601 format “2018-10-01” (or “2018-10-1”) as Mike already lined out.

Thank you! all i did was to change the “/” to “-” and it worked!