An item with the same key has already been added. : Error

 select 
 distinct
  L2HdrTxt,L3HdrTxt,LeafhdrTxt,L3HdrTxt as HD,
FullValue1 as IncFV,FullValue_OPI,fullValue_Opm,FullValue_Osy,FullValue_PFC,
FullValue_PRO,FullValue_ZTL,FullValue_ELM,FullValue_CYX,Full_Value,TotalYTDlessDep,ELMLessDEP,ZTLLessDep,PROLESSDEPP,PFCLessDep,PFCLessDep
,OSYLESSDEP,OPMLESSDEP,OIDLESSDEP
from Vw_Consolidated_Period_Range_G_A

I cannot update the above query into my report dataset.. I get the error message  An item with the same key has already been added. I have done some research and to my avail its not helping me.. I have changed the col names and all.. Can someone guide me ?

FM