Thank you. It seems to be solved. File\options\save were set to .xlsx, but it was saving as xls.
If you have a minute can you tell me about the two "--" that you added after the = to the formula? Is there a link that explains what those do?
=--(INDEX('Cycle Analysis'!C$3:C$1215,MATCH($B3,'Cycle Analysis'!$B$3:$B$1215,0))="Y")