Class DistutilsClassError

              object --+            
                       |            
exceptions.BaseException --+        
                           |        
        exceptions.Exception --+    
                               |    
                  DistutilsError --+
                                   |
                                  DistutilsClassError

Some command class (or possibly distribution class, if anyone feels a need to subclass Distribution) is found not to be holding up its end of the bargain, ie. implementing some part of the "command "interface.