How to use setwb?

Say I have an already fully configured Neural Network net. I am trying to write the algorithm for the cascade k-fold cross validation of this network. For the first fold I initialize the weights randomly (using initnw). I would like all following folds to get the weights that resulted from the training of the previous fold using initwb and setwb. The relevant code snippet looks like the following:

for i=1:numberOfFolds
    if (i==1)
        net = init(net); % Random initialization
    else
        % bestIW{i-1} and bestLW{i-1} are the net.IW and net.LW 
        % of the best trained network of the previous fold
        net.layers{1:end}.initFcn = 'initwb';
        net = setwb(net,[bestIW{i-1},bestLW{i-1}]);
    end
end

When I run the full code I get the following error message:

Index exceeds the number of array elements (12).

I'm not sure how to format the second arguement of the setwb command in order for this to work. Also, do I need to run init(net) after setwb?