Message type: E = Error
Message class:  CNV21500 - Messages for HR conversions basis 
Message number: 020
Message text: Structure &1 of component &2 is not defined in DDIC.
Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of messages in the SAP system have a message text, however this is frequently insufficient to comprehend or resolve the problem.
To make things easier, more detailed information is frequently added to describe the issue, how to fix it, and the necessary steps or configuration modifications.
Unfortunately, there isn't any extra information in this error notice.
First, use our AnswerBot below to get a possible cause and solution (requires a premium subscription).
Also, review the in-depth Common Questions & Answers listed below; you could discover a solution there or be able to connect with others who have faced similar challenges.
You can also try searching the SAP support portal (support.sap.com) but you need a special user ID to access it. It is possible that an SAP support note exists that provides additional details about the mistake or even steps for fixing it.
The SAP error message CNV21500020 indicates that a specific structure (denoted as &1) of a component (denoted as &2) is not defined in the Data Dictionary (DDIC). This error typically arises during data migration or conversion processes, particularly when using SAP's tools for data migration, such as the SAP S/4HANA Migration Cockpit or other conversion tools.
Cause: Missing Structure Definition: The structure that the system is trying to access does not exist in the Data Dictionary. This could be due to: The structure not being created or activated. The structure being deleted or not transported correctly from the development environment to the production environment. A mismatch in the version of the component being used. Incorrect Configuration: The configuration settings for the migration or conversion process may be incorrect, leading the system to look for a structure that is not available. Transport Issues: If the component was recently transported, there may have been issues during the transport process
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
CNV21500019 No info about &1 in CNV_INDX_STRUC.
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV21500018 Import/export macro &1 not defined for relid <&2,&3>.
What causes this issue?  Import/export macro &v1& not defined for relid <&v2&,&v3&>. This means that import/export macro...
CNV21500021 Structure &1 of component &2 found in DDIC.
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV21500022 Declaration of component &1 not found includes for RELID <&2, &3>.
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
Click on this link to search all SAP messages.