Changing Opportunity:The Document could not be saved.

Hi,Everyone!

     I have got a request to changing sales opportunity,so I tried to use Function Module 'BAPI_OPPORTUNITY_CHANGEMULTI'.If I flag TESTRUN = 'x',It run normally.But I  flag TESTRUN = SPACE.It return message 'The Document could not be saved' .It had  confused me.Please anyone help me.Thank you!

As below,my test program source:

REPORT  YTEST.

DATA:LT_HEADER TYPE STANDARD TABLE OF BAPIBUS20001_HEADER_UPD,

            LW_HEADER TYPE BAPIBUS20001_HEADER_UPD,

            LT_PARTNER TYPE STANDARD TABLE OF BAPIBUS20001_PARTNER_INS,

            LW_PARTNER TYPE BAPIBUS20001_PARTNER_INS,

            LT_INPUT_FIELDS TYPE STANDARD TABLE OF BAPIBUS20001_INPUT_FIELDS,

            LW_INPUT_FIELDS TYPE BAPIBUS20001_INPUT_FIELDS,

            LT_RETURN TYPE STANDARD TABLE OF BAPIRET2,

            LW_RETURN TYPE BAPIRET2.

LW_HEADER-GUID = 'E1198B5ED59B06F1A107984BE1014782'.

*LW_HEADER-OBJECT_ID = '2057'.

APPEND LW_HEADER TO LT_HEADER.

LW_PARTNER-REF_GUID = 'E1198B5ED59B06F1A107984BE1014782'.

LW_PARTNER-PARTNER_NO = '0080006382'.

APPEND LW_PARTNER TO LT_PARTNER.

LW_INPUT_FIELDS-REF_GUID = 'E1198B5ED59B06F1A107984BE1014782'.

LW_INPUT_FIELDS-REF_KIND = 'A'.

LW_INPUT_FIELDS-OBJECTNAME = 'PARTNER'.

LW_INPUT_FIELDS-FIELDNAME = 'PARTNER_NO'.

LW_INPUT_FIELDS-CHANGEABLE = 'X'.

APPEND LW_INPUT_FIELDS TO LT_INPUT_FIELDS.

CALL FUNCTION 'BAPI_OPPORTUNITY_CHANGEMULTI'

   EXPORTING

     TESTRUN                = SPACE

   TABLES

     HEADER                  = LT_HEADER

     PARTNER               = LT_PARTNER

     INPUT_FIELDS      = LT_INPUT_FIELDS

     RETURN                 = LT_RETURN.