Wow I am really baffled after upgrading to Microsoft 365 Excel.

Formulas don't calculate in my Windows 10 64 bit machine.

A simple index/match formula gives me the same result in a column. Whereas on my Windows XP Excel 2010 the same formula works to perfection.

Not sure if this is the reason but I have both Excel 2010 and Excel 365 installed on the same Windows 10 computer.

Any ideas on why the formula will not calculate?

The formula example, index($A$1:$A$100, Match($C1,$B$1:$B$100,0)) Cell C1 = ACD