Message type: E = Error
Message class:  FKK_ID_XX_ODN - ODN message 
Message number: 028
Message text: Number group assigned to the document class &1
You tried to change or delete the number group but the number group has
been already assigned to the document class in Customizing.
The system issues an error message and will not allow you to continue with this transaction until the error is resolved.
In the Customizing activity
<DS:SIMG._FICAOD_ODNNR_DET>Assign Number Range to Document Classes</>,
remove the current number group (sub object) assignment to the document
class. Only then you will be able to change or delete the number group.
Error message extract from SAP system. Copyright SAP SE.
The SAP error message FKK_ID_XX_ODN028 typically indicates that there is an issue with the number range assignment for a specific document class in the SAP system. This error occurs when the system cannot find a valid number range for the document class specified in the error message.
Cause: Missing Number Range Assignment: The document class does not have a number range assigned to it in the configuration. Inactive Number Range: The number range assigned to the document class may be inactive or not properly defined. Authorization Issues: The user may not have the necessary authorizations to access or use the number range. Configuration Errors: There may be errors in the configuration settings related to the number range or document class.
Solution: Check Number Range Configuration: Go to the transaction code OAVN (for number range objects) or OBA7 (for number range management). Verify that the number range for the specific document class is defined and active. If it is missing, create
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