How To Fix ARUN_MAIN042 - Item &1 is assigned; cannot change &2 in sch. line &3 (see long text &4)

SAP Error Message - Details

• Message type: E = Error

• Message class: ARUN_MAIN -

• Message number: 042

• Message text: Item &1 is assigned; cannot change &2 in sch. line &3 (see long text &4)

What causes this issue?

The material is relevant to Supply Assignment (ARun) and an assignment
exists for this document item.
You cannot change the document item for one of the following reasons:
The unassign rule field check is set to <ZK>Error </>in Customizing
under <LS>Cross-Application Components > Advanced Available-to-Promise
(aATP) > Supply Assignment (ARun) > Cross-Applications</>.
The item is already assigned; therefore, the material cannot be changed.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

You can set the field check from Error to one of the following options.
N = No Action
W = Warnings Before an Order is Unassigned
For application types (purchase orders, inline confirmations, and
inbound deliveries), you can set the Customizing under <LS>Cross-
Application Components > Advanced Available-to-Promise (aATP) > Supply
Assignment (ARun) > Cross-Applications > > Purchase Order Handling</>.
For application types (stock transport orders), you can set the
Customizing under <LS>Cross-Application Components > Advanced
Available-to-Promise (aATP) > Supply Assignment (ARun) >
Cross-Applications > Stock Transport Order Handling</>.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.

Smart SAP Assistant

• What is the cause and solution for SAP error message ARUN_MAIN042 - Item &1 is assigned; cannot change &2 in sch. line &3 (see long text &4) ?

  The SAP error message ARUN_MAIN042 indicates that there is an issue with changing a scheduled line in a sales order or a similar document because the item in question is already assigned to a specific schedule line. This typically occurs in the context of sales and distribution (SD) or materials management (MM) modules.
  
  Cause:
  The error arises when you attempt to change a characteristic of a scheduled line (like quantity, delivery date, etc.) for an item that is already assigned to a schedule line. This can happen due to:
  
  Existing Assignments: The item is already linked to a specific schedule line, and the system does not allow changes to certain fields while the assignment exists.
  Data Integrity Rules: SAP enforces data integrity rules to prevent inconsistencies in the scheduling and delivery processes.
  Locked Records: The item or schedule line may be locked by another transaction or user, preventing changes.
  
  
  Solution:
  To resolve this error, you can take