From the message, you got back only 3 items in that list.
To avoid the error, test length of list before trying to select item numbers from that list.
              
              
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            Welcome Hector.
The ImageClassifier only returns the probability percentages for the three highest regardless of the number of 'labels'--classifications.  It appears you tried to get four probabilities. 
You might find this discussion helpful: Personal image classifier display - #2 by SteveJG
