Can't get rid of item in viewport

I have this weird ‘line’ with a DOT in its center,and when I click on the DOT,it highlights the skylight, but when I DEL the skylight hoping to get rid of this odd object , the object remains.

What on earth is it, and how do I get rid of it while obviously wanting to preserve my level :wink:

TY- pls see PIC showing the problem