error on changing status "The document could not be saved" CRM_ORDER 037

hi,

i tried to change a a custom transaction type's item status by calling:

CALL METHOD cl_crm_isu_order_change=>set_single_status
        EXPORTING
          iv_guid        = l_quot_item-guid
          iv_status      = l_stat-estat
        RECEIVING
          ev_success     = l_success
        EXCEPTIONS
          error_occurred = 1
          OTHERS         = 2

this executes correctly as data is correct . but later,

CALL FUNCTION 'BAPI_BUSPROCESSND_SAVE'
           TABLES
             objects_to_save = lt_save
             saved_objects   = lt_saved
             return          = lt_return.
  gives error in return bapi message. so obviously,  'BAPI_TRANSACTION_COMMIT' does not work.

instead of first method, i tried crm_order_maintain also... but I get error while saving. i have also tried 'CRM_ORDER_SAVE' but save did not happen.

could you help, what could be wrong?