Error on ActiveGraph class application

[Frank Lin]

Hi,
 1. The following message is obtained from createing ActiveGraph object.

*** event raised for error: InvalidCombination
ActiveGraph not initialized properly*** execution terminating due to error
IOT trap

 2. The source code for the creation of ActiveGraph object is as follows:
 --------
  BLTGraph *mflowGraph;
  GraphElement *materialElement;
  ActiveGraph  *mflowGrapher;
  
  StatusM *statusM;
    
  mflowGraph = [BLTGraph create: globalZone];
  [mflowGraph title: "Matrial Flow vs. Time"];
  [mflowGraph axisLabelsX: "time" Y: "Material Flow"];
  [mflowGraph setWidth: 400 Height: 250];

  materialElement = [mflowGraph createElement];
  [materialElement setLabel: "Shipment of Products"];
  [materialElement setColor: "red"];
  
  mflowGrapher = [ActiveGraph createBegin: globalZone];
  [mflowGrapher setElement: materialElement];
  [mflowGrapher setDataFeed: statusM]; 
  [mflowGrapher setIntAccessor: M(getM)]; 
  mflowGrapher = [mflowGrapher createEnd];
  [mflowGraph pack];
----------

3. In which the statusM object is defined as follows:
 
@interface StatusM: SwarmObject
-(int) getM;
@end

@implementation StatusM
-(int) getM {
 return partSINK;
}
@end

4. Where is the problem with the ActiveGraph object creation?  Could someone 
give me a hint.

Frank