Help BAPI_MATERIAL_SAVEDATA !?!?

Hi Friends,

I've created a program that allow to change the <b>unit of measure</b> of a material master (add new  unit <b>USE</b>). But  wrong when I used BAPI  BAPI_MATERIAL_SAVEDATA to do it. The message error as below:

"specify the conversion factors for the unit of measure <b>USE</b>"

Anyone can tell me why?

Thanks,

Gy