ANN using nprtool for classification using "Firefly algorithm"

I am trying to train my ANN using nprtool in matlab for classification using "Firefly algorithm". This not being an in-built function, I am using the following line of code to train it :

      net.trainfcn='firefly_simple'.

But this gives the following errors :

??? Error using ==> rand Output class must be 'single' or 'double'.

Error in ==> firefly_simple>init_ffa at 96 xn=rand(1,n)*xrange+range(1);

Error in ==> firefly_simple at 62 [xn,yn,Lightn]=init_ffa(n,range);

Error in ==> network.subsasgn>setTrainFcn at 2111 net.trainParam = feval(trainFcn,'pdefaults');

Error in ==> network.subsasgn at 481 [net,err]=setTrainFcn(net,trainFcn);

Please suggest a solution to the problem. Thanks !!

P.S. firefly_simple.m is the open source matlab code available on Mathworks.