I have a circle centre sitting in the middle of the drawing that does not appear to be associated with any arc in the drawing.
Probably a remnant of a construction sequence.
Ordinary deletion doesn't work.
I have identified which layer it is on.
I there any way of systematically cleaning a drawing of these sorts of anomalies ?
I don't know of an automatic clean-up process.
What does "Properties" say? Maybe radius = 0? Linetype = No Pen?
Does "Select All" and "Auto Zoom" show the associated arc?
What kind of deletion does work?
Maybe you can delete everything else, so isolate that entity and save as an extra file. If you provide that file maybe someone finds out what's wrong.