Business Partner Classification - BAPI_OBJCL_CHANGE

Hi gurus,

I'm trying to use the following function to update the business partners classification.

CALL FUNCTION 'BAPI_OBJCL_CHANGE'

EXPORTING

   objectkey                = wa_objectkey

   objecttable              = 'JGVGPKLASS'

   classnum                 = 'CLIENTI'

   classtype                = '071'

*   STATUS                   = '1'

*   STANDARDCLASS            =

*   CHANGENUMBER             =

*   KEYDATE                  = SY-DATUM

*   NO_DEFAULT_VALUES        = ' '

* IMPORTING

*   CLASSIF_STATUS           =

TABLES

   allocvaluesnumnew        = gt_allocnum

   allocvaluescharnew       = gt_allocchar

   allocvaluescurrnew       = gt_alloccurr

   return                   = gt_return.

As a result I can add a characteristic to an existing classification, but I can not change a value for a characteristic already present in that classification.

I can not even delete a characteristic for that classification.

Can you give me directions about?

Thanks in advance.

Alessio