BAPI_CUSTOMERCONTRACT_CHANGE giving Update Error

Hi Friends,

I get an error 'Field header_inx-updateflag is not an input field' when calling the BAPI FM BAPI_CUSTOMERCONTRACT_CHANGE. I pass the 'U' flag to the Updateflag fields of the Header, Item and Condition and yet I get this error. When I debug I see the complete contract_header_inx structure in BAPI is filled where the Updateflag field is 'U' and the other fields to be changed is 'X'. When debugging the FM

after the CALL FUNCTION 'DIALOG_SET_NO_DIALOG'. The MOVE-CORRESPONDING CONTRACT_HEADER_IN TO DA_CONTRACT_HEADER_IN.

MOVE-CORRESPONDING CONTRACT_HEADER_INX TO DA_CONTRACT_HEADER_INX.

where the structure DA_CONTRACT_HEADER_IN shows data but DA_CONTRACT_HEADER_INX does not contain anything...whereas program my program when it passes the structure is filled. Thanks for your help