Question: system of partial differential equations with initial conditions

Hi

I'de like to see the solutions of the system of equations :

   restart
>
> with(PDEtools);

> eq := [diff(s(x, t), t) = -.35*i(x, t)*s(x, t), diff(i(x, t), t) = .35*i(x, t)*s(x, t)-.2*i(x, t)+.65*(diff(i(x, t), x))];

> cdt := {s(x, 0) = x, i(x, 0) = 0, s(0, t) = 0};

> sol := pdsolve(eq, cdt, [s, i], numeric, time = t, range = 0 .. 10);

> Splot := sol:-plot(s(x, t), t = 4, numpoints = 50, colour = red); Iplot := sol:-plot(i(x, t), t = 8, numpoints = 50, colour = green); plots[display]([Splot, Iplot]);

But I receive the error :

Error, (in pdsolve/numeric/plot) unable to compute solution for t>0.:
matrix is singular
Error, (in pdsolve/numeric/plot) unable to compute solution for t>0.:
matrix is singular
Error, (in plots:-display) expecting plot structures but received: [Splot, Iplot]

I don't know how i can do :/ Can you help me ? Thanks

P.S : Sorry for the english errors, i'm french :p