RapidMiner: does not have sufficient capabilities for handling an example set with only one label

_woken version: 9750bdc
woken-validation version: 9750bdc
knn version: 0.2.1 or naive-bayes version: 0.2.0_

When running RapidMiner algorithms on some co-variables with no sufficient data i guess (e.g. : leftcerebralwhitematter), RapidMiner complains that: does not have sufficient capabilities for handling an example set with only one label