Question regarding error "x and y lengths differ"

Hello, I'm a first semester statistics
student<http://r.789695.n4.nabble.com/Question-regarding-error-quot-x-and-y-lengths-differ-quot-td4665773.html#>and
I am using R for roughly the third time ever. I am following a
tutorial
and yet I still get the error "x and y lengths differ." I am very new to
this program, and I have searched for solutions, but because I do not
understand the program too well, I am not sure which solution may apply to
me. Any help is much appreciated!

The question is as follows:

Do this given your population standard deviation. If we pick a confidence
interval, say ?
= 0.1(90% confidence), we can compute a confidence interval for our measure
of the
population mean for each one of our samples. Now let?s compute and plot the
confidence intervals for the 50 samples:>  m = 50; n = 40; mu = mean(pop);
sigma = sd(pop);

SE = sigma/sqrt(n) # Standard error in mean
alpha = 0.10 ; zstar = qnorm(1-alpha/2); # Find z for 90%

confidence

matplot(rbind( samp_mean - zstar*SE, samp_mean +

zstar*SE),rbind(1:m,1:m), type="l", lty=1);

abline(v=mu)

I am receiving the error "Error in xy.coords(x, y, xlabel, ylabel, log =
log) :
   'x' and 'y' lengths differ" when inputting>matplot(rbind( samp_mean -
zstar*SE, samp_mean +
zstar*SE),rbind(1:m,1:m), type="l", lty=1);