Key Field missing in transformation

Hi

I am trying to use BI7.0 transformation (1-1 mapping basically) to send data from one DSO to another DSO

Source : DSO1

Key fields : Account ,Itemid, Position number

Target: DSO2

Key fields : Account ,Itemid, Position number

However when i create transformation i don't see "Itemid" in the source side in the transformation mapping. Rest of the two key fields are present.

Please help.

-Anurag