GNU Octave Vertical Dimensions Mismatch - octave

Question

I've been getting the following error in GNU Octave:
error: vertical dimensions mismatch (1x2 vs 1x3) error: called from
ProjectPart1 at line 31 column 4
based on this code (in a for/end loop after zeta(:,1)):
zeta(:,1)=[sum(beta)/lambda,P0];
N=[-lambda,sum(beta);lambda/gen,(rho-sum(beta))/gen];
zeta(:,i)=zeta(:,i-1)+N*zeta(:,i-1)*dt;
I ran this a month-ish ago and I remember it working, any idea why it's not working now?
Edit:
Here's the whole thing. I've tried switching things around, restarting the program, and restarting my computer. Is uninstalling and reinstalling worth it (since one commenter said it worked fine for them)?
lam=[0.0128,0.0318,0.119,0.3181,1.4027,3.9286];
beta=[0.000258,0.00152,0.001391,0.00307,0.001102,0.000258];
P0=1e-6;
a=8*sum(beta);
lambda=((beta(1)*lam(1))+(beta(2)*lam(2))+(beta(3)*lam(3))+(beta(4)*lam(4))+(beta(5)*lam(5))+(beta(6)*lam(6)))/sum(beta);
hold off;
box on;
gen=2.6E-5;
dt=.001;
secint=.125/dt;
t(1)=0;
zeta(:,1)=[sum(beta)/lambda,P0];
rho(1)=0
for i=2:secint
N=[-lambda,sum(beta);lambda/gen,(rho-sum(beta))/gen];
zeta(:,i)=zeta(:,i-1)+N*zeta(:,i-1)*dt;
t(i)=t(i-1)+dt;
rho(i)=a*t(i);
end
The vertical dimensions error is specifically pointing to this line:
N=[-lambda,sum(beta);lambda/gen,(rho-sum(beta))/gen];