After blocking, when the user do a inventory posting, they will get this error message :-
E: Material xxxxx has status Blocked for procmnt/whse
To activate the blocking :-
Goto transaction MM02 - Purchasing View
Type in 01 at the MM/PP status field and save it
Create Delivery Log - Material xxx is blocked
During the Create Delivery (VL01), SAP prompt you a log that Material xxx is blocked.
During the Sales Order Create/Change for that material, there might be some update termination that causes the locked of the material (Windows hanged or power failure).
You can check using transaction SM12 - type an "*" at the User name field.
Check whether the material is in the locked list.
If it is in the locked list, asked the user to log out before you delete it from the locked list.