CALL TRANSACTION not working as expected

Hi All,

wa_item-vbeln = '0180000053'.

SET PARAMETER ID 'VL' FIELD wa_item-vbeln.

CALL TRANSACTION 'VL33N'.

I am having an issue with the above code. For some reason it won't pass the document number through to transaction VL33N.

Is there any reason for this?

Many Thanks,

Colm