Message type: E = Error
Message class:  CNV_MBT - PCL message class 
Message number: 142
Message text: Activity ID & phase & does not exist in the IMG of package &
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_MBT142 typically indicates that there is an issue related to the configuration of a specific activity in the Implementation Guide (IMG) for a package. This error often arises during the execution of a migration or conversion project, particularly when using the SAP S/4HANA Migration Cockpit or similar tools.
Cause: Missing Activity ID: The specified Activity ID does not exist in the IMG for the package you are working with. This could be due to: The activity not being defined in the system. The activity being deleted or not yet created. A mismatch between the expected and actual configuration in the IMG. Incorrect Package: The package specified may not be the correct one for the activity you are trying to execute. Transport Issues: If the configuration was transported from another system, it may not have been transported correctly, leading to missing activities.
Solution: Check IMG Configuration: Go to the Implementation Guide (IMG) and verify if the Activity
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
CNV_MBT141 & inconsistencies found in copy variant &
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_MBT140 Checking copy variant & for package &
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_MBT143 You can choose only one action per copy rule
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_MBT144 Delete action requires the acticity ID
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.