How to plot a confusion matrix ?

Dear Matlab experts,

I have a issue with this function:

plotconfusion(Ytest.grade,app.predict)

When I put the tow vectors into categorical I have this error:

And when i put the two vectors into double I have again an error:

So how can I plot this confusion matrix then ?

NB: the function

app.confusionMat = confusionmat(Ytest.grade, app.predict);

works perfectly well !

Many thanks in advance !

Pierre