@ IVAN & TARUNA :-
This problem you are facing for your User might be due to the authorization rights set for your user.
Please login as super user and goto.
For Unit Price :-
Administration --> System Initialization --> Authorizations --> Sale A/R --> Change Raw Amount (Give the Full Authorization).
Now Choose your user from the list and check the authorizations set in Purchasing A/P.
For Quantity :-
Login with User(Logistic) in SAP and Check the form Setting for Quantity field should be active.
Thanks