Billing Doc and Billing Item missing in 2LIS_13_VDITM

Hi BI Experts,

Fields VBRP-VBELN and VBRP-POSNR are missing in 2LIS_13_VDITM data source.This data source has extract structure MC13VD0ITM which has includes MC13VD2ITM with VBELN field(Sales Document) and MC13VD5ITM with POSNR field(Sales Document Item).Because of these two includes,I am unable to add VBRP-VBELN and VBRP-POSNR fields in append structure of include MC13VD4ITM .The system is throwing error of duplicate entries with same name VBELN and POSNR fields during structure activation.

Please guide me how to rectify this error.

Thanks&Regards,

Venkat