an object that I can't delete

[JonD]

I have a strange little green object that is a bit outside the building that I am modelling. It's a green line about 1 meter long with a little spur sticking out of its mid point at 90 degrees. I can select it but I can't delete it. If I select it and right click, I don't get the option to open it so that I could see what type of object it is.

This is NOT an April 1st joke! Advice on zapping it is welcome.

[Katalyst777]

Sounds like a roof baseline to me.