whats is that error in matlab?

When I write this code, the matrix that is called (confusion matrix) does not appear to me .... But this shape appears and says these words and I do not understand the problem:

% load('P2.mat')

% load('P.mat')

% load('T.mat')

net=feedforwardnet(2);

net=train(net,P,T);

view(net)

P3=net(P2);

plotconfusion(T,P3)

[Star Strider]

You may have too many classes for plotconfusion to produce the optimal result.

The warning is just that — a warning. The best option is to restart MATLAB. (This can occur after graphics hardware driver updates.)

[Aya Ahmed]

Thank you very mach Star Strider , iam restart the matlab but stel the same error .

plz tel me , how can i know the number of classes ?

i want to make classification with images into three type of images so what I did was.... I made two matrices to train the images: [ One is the input matrix, called P, consisting of 236 rows * 120 columns features of images .The other is the Target matrix, called T, consisting of 120 rows * 120 columns].And a matrix for the test called P2 consists of 236 rows * 120 columns.

Is there anything wrong with that ?? Where are these Classes here?