I am trying to group a column of dates by year and month, and I've done
it before and it's worked fine. But now it's saying "Cannot group on
that Selection". I checked the data and it's in date format and there
aren't any blank or null values. It seems like this is a bug because
I've done it before with the same exact data. Have any of you had this
problem? What am I doing wrong?

Thanks!

Lis