Message type: E = Error
Message class:  CNV_PE_TPM - Messages within transport management functions 
Message number: 051
Message text: Transformation rule & 1 is not a value or extended value mapping
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_PE_TPM051 typically occurs during data migration or transformation processes, particularly when using the SAP Landscape Transformation (SLT) or SAP Data Services. This error indicates that a transformation rule specified in the mapping is not recognized as a valid value or extended value mapping.
Cause: Invalid Mapping: The transformation rule specified in the mapping does not exist or is incorrectly defined. Data Type Mismatch: The data type of the source value does not match the expected data type of the target value. Missing Values: The mapping may be missing required values or mappings for certain fields.
Configuration Issues: There may be issues with the configuration of the transformation rules or the mapping itself.
Solution: Check Transformation Rules: Verify that the transformation rule specified in the error message is correctly defined in the mapping. Ensure that it exists and is properly configured. Review Data Types: Ensure that the data types of the source and target fields
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
CNV_PE_TPM050 Transformation rule &1 cannot be loaded
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_PE_TPM049 Forward navigation only for Object Type Project
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CNV_PE_TPM052 Transformation rule &1 is not included (namespace)
What causes this issue?  The transformation rule with &V1& (ID &V2&) is <ZH>not </>included due to a namespace conflictSys...
CNV_PE_TPM053 Template include &1 is not found in the system
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.