Error using ==> plus Matrix dimensions must agree

I am really confused. I currently use a mod file that seemed to work nicely. But with a slight variation of the model, I still can compute an initial steady state and a final steady state, and the rank condition is still verified, but the following instructions:

stoch_simul(order=1,irf=0); //,nograph,noprint
forecast(periods=50,nograph);

lead me to the following error messages:

??? Error using ==> plus
Matrix dimensions must agree.

Error in ==> dr1 at 435
M1 = inv(f0+[zeros(M_.endo_nbr,nstatic)
f1*gx zeros(M_.endo_nbr,nyf-nboth)]);

Error in ==> resol at 128
[dr,info,M_,options_,oo_] =
dr1(dr,check_flag,M_,options_,oo_);

Error in ==> stoch_simul at 42
[oo_.dr, info] = resol(oo_.steady_state,0);

Error in ==> permanent_shock_theta1 at 587
info = stoch_simul(var_list_);

Error in ==> dynare at 132
evalin(‘base’,fname) ;

Please post the mod-file.