Question: How do I solve this problem?

hi friends

i have a problem in maple with an error

dx := diff(x(t), t, t) = -G*Mz*x(t)/(x(t)^2+y(t)^2)^(3/2):

dy := diff(y(t), t, t) = -G*Mz*y(t)/(x(t)^2+y(t)^2)^(3/2):

 G := 6.67*10^(-11); Mz := 6*10^24:
 IniC := x(0) = 7*10^6, (D(x))(0) = 0, y(0) = 0, (D(y))(0) = 9*10^3:
 Digits := 15:
 Ns := dsolve({dx, dy, IniC}, {x(t), y(t)}, numeric):
 dsnumsort(Ns(0), [x, y]);

>for i from 0 to 400 do T := 40*i; NsT := Ns(T); X[i] := rhs(NsT[C1]); Vx[i] := rhs(NsT[V1]); Y[i] := rhs(NsT[C2]); Vy[i] := rhs(NsT[V2]); MofI[i] := X[i]*Vy[i]-Y[i]*Vx[i] end do:

> with(plots);
> p1 := polarplot(6378*10^3, phi = 0 .. 2*Pi);
> p2 := plot([seq([X[i], Y[i]], i = 0 .. 327)], thickness = 2);

display({p1, p2}, labels = ['x', 'y'], scaling = constrained);

but i see and I I can't draw PLOT:

Error, invalid input: rhs received [t = HFloat(0.0), x(t) = HFloat(1.0), diff(x(t), t) = HFloat(0.0), y(t) = HFloat(0.0), diff(y(t), t) = HFloat(1.0), z(t) = HFloat(0.75), diff(z(t), t) = HFloat(0.0)][C1], which is not valid for its 1st argument, expr

can you helpe me?