I have a problem in evaluating machine learniong algorithms in WEKA!

I did the first six steps correctly, accordang to the instructions at https://machinelearningmastery.com/binary-classification-tutorial-weka/ but from step 7 I get the following:

7. Click on “Run” to open the Run tab and click the “Start” button to run the experiment. The experiment should complete in just a few seconds.

I got a report like this:

09:38:24: Started 09:38:24: Class atribute is not nominal! 09:38:24: Interrupted 09:38:24: There was 1 error

8. Click on the “Analyse” to open the Analyse tab. Click the “Experiment” button to load the results from the experiment.

In the window “Test output”, I have got this:

Tester: weka.experiment.PairedCorrectedTTester –G, 4,5,6, -D1 ... Analysing: Percent_correct Datasets: 0 Resultsets: 0 Confidence: 0.05 (two tailed) Sorted by: - Date: 3/19/20, 9:53AM Index 0 out of bounds for lenght 0.

9. Click the the “Perform test” button to perform a pairwise test-test comparing all of the results to the results for ZeroR.

The test did not start.

There are no changes nor results!!! Where is the problem? What was happened?