I am having problems with selecting the intersection point in a 2d drawing I have created from scratch. Sometimes it works first time but then when I try and place a circle on another another intersection in the same drawing it doesn't work. 

When I try and create a circle at an intersection and hover over it the only snap that appears is for placing it on a line. Even if I use quick snaps it can't find the intersection and defaults to a point near the origin of the drawing. Can anybody please help?