Unable to select/delete some lines in CAD

I converted a backclipped cross section (a thin 6" slice) to CAD. There were some lines that I did not want to show in the detail so I selected them and deleted them. But, behind those lines were other lines that cannot be selected or deleted.

Has anyone encountere similar behavior before? I thought that a x-section converted to CAD would allow all lines to be edited.

Thanks,

Dave

Dave,

Your Cross Section Lines layer is probably locked.