Following step-by-step your tutorial, in the last command I'm getting this error:

Any idea on how to fix this?

It's a nice example, thanks for sharing.

Just FYI, FisherIris dataset is in example data and is used in many places in docs.

ExampleData["MachineLearning"] // Grid

{
 {"MachineLearning", "BostonHomes"},
 {"MachineLearning", "FisherIris"},
 {"MachineLearning", "MNIST"},
 {"MachineLearning", "MovieReview"},
 {"MachineLearning", "Mushroom"},
 {"MachineLearning", "Satellite"},
 {"MachineLearning", "Titanic"},
 {"MachineLearning", "UCILetter"},
 {"MachineLearning", "WineQuality"}
}