error: Invalid MERGE-INTO statement: Update of Primary index or partition column is not allowed

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error: Invalid MERGE-INTO statement: Update of Primary index or partition column is not allowed

something new for me  - didn't use this clause in SQL before  but now need  convert to teradata: 

 

merge into tt_Pop as a
using tt_PHV as b  on a.id = b.id
when matched then
update set ID = b.id,NRW = b.NRW,DepositsSum = b.DepositsSum,
when not matched then
insert(ID,NRW,,DepositsSum,  First_DateID, Exit_DateID, ExitReason)
values(b.cd,b.NRW,b.DepositsSum,b., CAST(CAST(((CURRENT_TIMESTAMP)(FORMAT 'YYYYMMDD')) AS VARCHAR(100)) AS INTEGER),20990101,'NA');

 

it's not works - i get this  error:   Invalid MERGE-INTO statement: Update of Primary index or partition column is not allowed . 

 

any help, please!