Numerical output from "fit" function using a loop

Hello folks,

I have a matrix of water velocity data called ur10 (43x609), where there are 609 profiles at regular time intervals and 43 vertical depth bins per profile. I want to fit an exponential curve to the lowermost 4 bins of each profile, then pull out the coefficients (i.e. slope and y-intercept, here ustar and z0) of each line. My end goal is then to have two vectors, each 609 long, with all the slopes and y-intercepts. My code is below, but when I run it I get an error stating "Error using cfit/subsref. Too many output arguments." What do I need to change? I haven't used the "fit" function before so any advice would be much appreciated. I am using Matlab R2016b on a Macbook Pro. Thanks!

fitcoeffs=zeros(609,2);z0=zeros(609,1);ustar=zeros(609,1);
for i=1:609 %first 609 profiles go to z bin 41

      %calculate ustar using lowest 4 z bins
      [fit,gfit]=fit(ur10(38:41,i),z(38:41),'exp1');
      fitcoeffs(i)=coeffvalues(fit);
      z0(i)=fitcoeffs(i,1);
      ustar(i)=fitcoeffs(i,2);
  end

[Rik]

Please copy the entire error stack.