NAV User permission setup

Dear forum,
I am trying to set user Permission wherein My user will enter sales/Purchase order, and the same user will not be allowed to change in any master cards Like Item, Customer, Vendor etc…
I set RIMDX as following -
Object type-Table data, Object Name-ITEM, Permission = Y-I-I-I-Y
Object type-Table, Object Name-ITEM, Permission = Y-I-I-I-Y
After setting up above permission my user is not able to any change in Item Card which is OK and i wanted the same,
but user is not able to post his order also and finding message “you do not have permission to modify item table”.
so plz tell me where i me doing wrong??? I am using end user(Customer) license.

Thxn in advance

…because posting a PO updates ItemCard (read Item table) - Last Direct Cost field, for example, seemingly some more, don’t remember by heart.

I agree but how can i restrict my user for changing in item card with order posting rights.