Addition hours to timestamp

Hi BI/Abap gurus,

I am trying to add 8 hours based on the source fields mapped.

I have google around and the FM seems promising.

sample source fields-crm_due_dt: 20141120163000

And I have tested in SE37, seems to be fine.

but loading data causes error below:-

Any advice please?

CALL FUNCTION 'TIMESTAMP_DURATION_ADD'

       EXPORTING

         timestamp_in  = SOURCE_FIELDS-crm_due_dt

         timezone      = 'UTC'

         duration      = '8'

         unit          = 'H'

       IMPORTING

       timestamp_out   = RESULT.

Many thanks.