Message type: E = Error
Message class:  CNV_MBT_ME - Messages for Mapping Engine and Merge Simulation 
Message number: 003
Message text: Starting Merge Simulation for &1.
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 CNV_MBT_ME003, which states "Starting Merge Simulation for &1," typically occurs during the execution of a merge simulation in the context of data migration or data transformation processes, particularly when using the SAP S/4HANA Migration Cockpit or similar tools.
Cause:
Configuration Issues: The error may arise due to incorrect or incomplete configuration settings in the migration project. Data Quality Issues: There may be inconsistencies or errors in the source data that prevent the merge simulation from executing properly. Missing Authorizations: The user executing the merge simulation may lack the necessary authorizations to perform the operation. Technical Issues: There could be underlying technical issues, such as system performance problems or database locks, that hinder the simulation process.
Solution: Check Configuration: Review the configuration settings for the migration project to ensure that all required parameters are correctly set. Data Validation: Perform a thorough validation of the source data to identify and rectify any inconsistencies or errors. This
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
CNV_MBT_ME002 Simulation of table &1 did not generate log entries
What causes this issue?  The conversion of table &V1& was simulated and no log was written. This may be because the applied mappings did not c...
CNV_MBT_ME001 Duplicates found &1 &2 &3 &4
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_MBT_ME004 No duplicate keys found
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_MBT_ME005 Load of mapping &1 failed. Simulation is executed without this mapping
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.