fittype input argument error

Hi I am trying to run a code to fit a curve to some data. The code works on a colleagues version of Matlab. When I try to define the fittype using:

g = fittype( @(a, b, c, x) c*(x-a).*exp(-0.5*((x-a)/b).^2), ... 'independent', {'x'});

I get the following error:

Error using fittype (line 212) First input argument must be a string or cell array.

Any help greatly appreciated.