I would guess that one of those "Last Date Played" columns is an actual new MC field, which you created in "Tools>Options>Library and Folders>Manage Library Fields", and the other is just a column in your view. Maybe an Expression Column? In your other thread you just said, 'So I made a new field and called it "Last Date Played".' How did you create that field initially? I was able to duplicate your problem by creating an Expression Column in my view, and fix it as below.
Try right clicking on the row to see the columns displayed in the view. Untick both "Last Date Played" items. Get out of edit mode. Then go back into edit mode via right click and add the "Last Date Played" column again. There should be only one version of it now.
PS: I'm guessing a bit here as I don't know how you first created your "Last Date Played" field.