Failed to create a session; confirm that the user has the proper privileges to log on to Microsoft Dynamics

When you are going to prepare PO in Microsoft Dynamics AX 2012 following mentioned error is shown when you are going to add a new Item in a PO.
"Failed to create a session; confirm that the user has the proper privileges to log on to Microsoft Dynamics."



Follow the below mentioned procedure.
Open AOT workspace.
>Tools > Options > Development > Unmark "Execute business operations in CIL"
 


(or)

1) Stop the AOS
2) Restart the AOS

Now you can access the Item for prepare a Purchase Order in Microsoft Dynamics AX 2012.