SD-Pricing Conditions: Allowed Fields

Hi Guys

basic functions > pricing> condition table> conditions:allowed fields > new fields

when I try to add a new field: VOLEH ( selected using F4), system throwing following warning message: "Choose the key from the allowed namespace". We can save by ignoring this message.

But when I try to create condition table, this field is not visible.

Please suggest me how to add field VOLEH(Volume unit).

Regards

Uma