Can’t Delete Impreza Theme

I have the strangest problem. I cannot delete my Impreza theme. I get this error: Deletion failed: The requested theme does not exist.

It does exist & my website is using it! I can’t install an update to it because it won’t let me get rid of the old theme.

I went in and deleted the Twenty Fifteen theme to see if I could get rid of a different theme and had no problems deleting it.

I’m using WordPress 4.6.

Any help on this is much appreciated.