Error : Subscripted assignment dimension mismatch.

Hello everyone, I want to classify a list of 5 test images using the library LIBSVM with a strategy 'one against all' in order to obtain probabilities for each class. the used code is bellow :

      load('D:\xapp.mat');
      load('D:\xtest.mat');
      load('D:\yapp.mat');%%matrix contains true class of images yapp=[641;645;1001;1010;1100]
      load('D:\ytest.mat');%%matrix contains unlabeled class of test set  ytest=[1;2;3;4;5]

   numLabels=max(yapp);
   numTest=size(ytest,1);

    %# train one-against-all models
    model = cell(numLabels,1);
for k=1:numLabels
    model{k} = svmtrain(double(yapp==k),xapp, ['-c 1000 -g 10 -b 1 ']);
end

%# get probability estimates of test instances using each model
prob = zeros(numTest,numLabels);
for k=1:numLabels
  [~,~,p] = svmpredict(double(ytest==k), xtest, model{k}, '-b 1');
  prob(:,k) = p(:,model{k}.Label==1);    %# probability of class==k
end

   %# predict the class with the highest probability
[~,pred] = max(prob,[],2);
acc = sum(pred == ytest) ./ numel(ytest)    %# accuracy

I obtain this error :

    Model does not support probabiliy estimates
    Subscripted assignment dimension mismatch.

     Error in comp (line 98)
      prob(:,k) = p(:,model{k}.Label==1);    %# probability of class==k

please, help me to solve this error and thanks in advance