Message type: E = Error
Message class:  CNV_CMIS_A_20 - Message class for Cross-Client Customizing Comparison (SLO) 
Message number: 501
Message text: Changes will be lost
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_CMIS_A_20501 with the description "Changes will be lost" typically occurs during data migration or conversion processes, particularly when using the SAP S/4HANA Migration Cockpit or similar tools. This error indicates that there are unsaved changes in the data that you are trying to process, and if you proceed, those changes will be lost.
Cause: Unsaved Changes: The most common cause of this error is that there are unsaved changes in the data entry fields or in the migration cockpit that you are working on. Session Timeout: If the session has timed out, any changes made may not be saved, leading to this error when trying to proceed. Data Validation Issues: Sometimes, the error can also arise if there are validation issues with the data being processed, which may prevent the system from saving changes.
Solution: Save Changes: Before proceeding with any action that triggers this error, ensure that you save all changes
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
CNV_CMIS_A_20311 Select at least one special analysis type
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_CMIS_A_20310 Included big Table list excluded succcessfully
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_CMIS_A_20502 Changes are saved
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_CMIS_A_20871 Select a table to be excluded from content comparison
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.