Unable to assign category code

Hi,
We are trying to change category codes , old category was Telco.airtime.rcvs and we are trying to change to 01.1000.rcv200

Previously we were having rcv's under telco.airtime.rcvs but now we are differentiating seperatley each one as 01.1000.rcv200,01.1000.rcv1000

we have item_type(independent), item_categories(depended),item_sub_category(independent)

Here we are facing problem, when we are assigning this new code combination in category code we are getting
error: value item_category for the flexfield segment category does not exist in the value set item_category(value=1000)
and unable to define new category.

Thanks
Vinay