Geom2dAPI_InterCurveCurve Problem

Hi,
There are two 3D curves, I project them to a plane. I use Geom2dAPI_InterCurveCurve to find NbPoints but the result is zero. Therefore I export them to iges and then import it, and try Geom2dAPI_InterCurveCurve again, the NbPoints is one. So,I use the other CAD/CAM software to find their intersecion point, I found the intersection point is very close to the end point of the one of the curve and the distance is about 0.1 mm. Is it bug on OCC5 or my way is wrong? my code as following,

Geom2dAPI_InterCurveCurve IntCC(c1,c2);
Standard_Integer n=IntCC.NbPoints();

Sincerely,
Angel