accessviolationexception was unhandled

unsafe
         {
             for (i = 0; i < Math.Min(lines.Total, 100); i++)
             {

                 float* line = (float*)lines.GetSeqElem<IntPtr>(i).Value.ToPointer();

                 float rho = line[0]; <= I got the error here

                 float theta = line[1];
                 CvPoint pt1, pt2;
                 double a = Math.Cos(theta);
                 double b = Math.Sin(theta);
                 double x0 = a * (rho);
                 double y0 = b * (rho);
                 pt1.X = Cv.Round(x0 + 1000 * (-b));
                 pt1.Y = Cv.Round(y0 + 1000 * (a));
                 pt2.X = Cv.Round(x0 - 1000 * (-b));
                 pt2.Y = Cv.Round(y0 - 1000 * (a));
                 Cv.Line(des, pt1, pt2, Cv.RGB(255, 255, 255), 3, Cv.AA, 0);


             }