Can't Send to Trasn the Status

Hi, I’m trying to delete one of unused status in the Admin menu > Status List, but ShotGird says ‘Please go remove this status from those fields first before sending to trash.’
I looked both Asset and Task entity and none of the items has status which I’m trying to remove.
I do want to keep Status field, and just want to delete one of status item.

I figured how.
In both Asset and Task page’s Status field, right click > Configure Field > Click trash box icon > Update Field > Remove Status.
Then from Admin menu > Status List > select status > More > Send Selected Status to Trash.