display

 i have one pick manipulation  renderer 'pmr' , two data references
ref2,ref3, and one constant Map 'Alpha_CMap' in one display;

i want to add the constant Map and pmr to the whole display, 
so i do: 
 display2.addReferences(pmr,ref2); 
 display2.addReferences(pmr,ref3); 
 display2.addReference(ref3,Alpha_CMap); 
 display2.addReference(ref2,Alpha_CMap); 

i get the exception below: 

visad.TypeException: DisplayImpl.addReference: link already exists 
at visad.DisplayImpl.addReference(DisplayImpl.java:827) 

is there a way to add the pmr , Alpha_CMap to the display and the two data
references ? 
i am not sure if i will need direct manipulation instead; 

thanks, 

Isaac