Passing KFold to any classification model creates a ClassificationPartitionedModel, which is a set of multiple models. As such, one cannot call predict on it. Instead, you can use kfoldPredict function, which gives you the classification accuracy on the training partition for each of the model. For example,
load fisheriris.mat
mdl = fitcdiscr(meas, species, 'DiscrimType', 'quadratic', 'KFold', 4);
kfoldPredict(mdl)
If you want to predict on test dataset, train a separate model with same parameters, except for KFold, and then use predict on the test dataset.
The error message is a known issue, and might be fixed in any of the upcoming releases.
