I can't draw vector plot with octave

[c]

gnuplot_binary=c:/gp371w32/pgnuplot

gnuplot_has_multiplot=1

page_output_immediatery=1

ans=:/usr/local/share/octave/2.1.39/m/statistics//:/usr/local/share/octave/2.1.39/m/control//

octave:1 > function g = G(s)
              g = (1.+s)./(1.+21.*s);
              endfunction
octave:2 > w = logspace(-2, 4, 300);
octave:3 > s = G(j.*w);
octave:4 > grid "on"
octave:5 > Can't find the gnuplot windows

warning: connection to external plotter (pid=yxxxxxx) lost -- 

warning: please try your plot command(s) again

octave:6 > plot(real(s), imag(s))

(I can't read and write  because too many error,  warning, and functional messages)

 

Because of it, I can't make "gnuplot" appear the graph I want.

Sometimes, octave says "Time out gnuplot" when I write "grid on" 

The word "yxxxxxx" stands for a number(y=3or4 xxxxxx=random 6-figure number)

What's wrong?  Which is wrong, octave or myself?