Transfer function and graphic (Scilab error)
Sorry to point this out, but it seems that you are using the Matlab notation and have not even looked at the Scilab language reference, still,

clc; 
clear all;
xdel(winsid())

A=[-1 -2;42 -0.9]
B=[1.5;1.1]
C=[0.7 2.1]
D=[0]
H=syslin('c',A,B,C,D)
H=ss2tf(H)
figure
t=0:0.05:5;
plot(t,csim('step',t,H))
xgrid(2)