Matrix access isn't working correct

edit savecancel

I have the following code snippet

Mat label_features(10,1,CV_8UC1);

for(int i = 0; i < 10; i++){
    label_features.at<int>(i,0) = 1;
}

For some reason, this gives a problem when creating and adding values to the matrix. Please ignore the fact that I am adding a '1' value here. It could basically be any value between 0 and 255.

Anyone can tell me why i get the following violation?