How to fit exponential function to data by appointing custom fittype

I am trying to fit an exponential model to my data in the form of a*(1-exp(-b*x)). After some searching i found the following code:

x=data(:,1);
y=data(:,2);
g = fittype('a*(1-exp(-b*x))');
xx = linspace(min(x),max(x),length(x));
f0 = fit(x,y,g,'StartPoint',[[ones(size(x)), -exp(-x)]\y);
plot(x,y,'o',xx,f0(xx),'r-');

Here 'data' (at least a part of it) is presented (txt file) in the attachment for an increasing and decreasing system. However, i can't seem to get it working properly. for f0 an error pops up regarding the amount of start point, but after putting

f0 = fit(x,y,g,'StartPoint',[[ones(size(x)), -exp(-x)]);

an error pops up stating 'Matrix must be column or row vector'

please advise.

Thanks in advance