Sequence of stochastic shocks

I want to simulate a sequence of stochastic shocks (on the same variable). That is, first shock, then use the irf at t=1 as initval for the second shock, and so on… Do you think it’s ok? I tried but dynare gives me the following error that I don’t understand:

??? Attempted to access x(2); index out of bounds because numel(x)=1.

Error in ==> model_simple_r_static at 24
rhs =y(4)+x(2)+y(6);

Error in ==> resol at 130
resid = feval(fh,steady_state_0,oo_.exo_steady_state, M_.params);

Error in ==> stoch_simul at 66
[oo_.dr, info] = resol(oo_.steady_state,0);

Error in ==> model_simple_r at 285
info = stoch_simul(var_list_);

Error in ==> dynare at 120
evalin(‘base’,fname) ;

Can someone help? Thanks