How To Fix CL520 - Only one class can be selected as a standard class

CL520 - Overview

• Message type: E = Error

• Message class: CL - Classification

• Message number: 520

• Message text: Only one class can be selected as a standard class

What causes this issue?

You have selected more than one class as
<DS:GLOS.standard_class>standard class</> for an object. This is not
allowed.

System Response

The last classes you selected are automatically deselected by the
system.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.

CL520 - Details

• The SAP error message CL520, which states "Only one class can be selected as a standard class," typically occurs when you are trying to define or modify a class in the SAP system, particularly in the context of class hierarchies or when dealing with class types.
  
  Cause:
  This error arises when you attempt to assign more than one class as a "standard class" in a given context. In SAP, a standard class is a class that serves as a reference or base class for other classes. The system enforces the rule that only one class can be designated as the standard class to maintain a clear and unambiguous class hierarchy.
  
  Solution:
  To resolve this error, you should follow these steps:
  
  
  Check Existing Classes: Review the classes that are currently defined in the system. You can do this by navigating to the class definition in the SAP GUI (transaction code CL02 for display or CL01 for