Message type: E = Error
Message class:  CNV10400 - Messages for package 10400 (characteristics) 
Message number: 666
Message text: Attribute conversion is active for Char. &.
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The SAP error message CNV10400666 indicates that there is an issue related to attribute conversion for a characteristic in the context of data migration or conversion processes, particularly when using the SAP Landscape Transformation (SLT) or SAP Data Services.
Cause: The error typically arises when: Attribute Conversion is Active: The system is trying to convert attributes for a characteristic that is not properly configured or is incompatible with the conversion rules defined in the system. Data Inconsistencies: There may be inconsistencies in the data being processed, such as missing values or incorrect formats.
Configuration Issues: The settings for the characteristic in question may not be correctly defined in the system, leading to issues during the conversion process.
Solution: To resolve this error, you can take the following steps: Check Configuration: Review the configuration settings for the characteristic in question. Ensure that the attribute conversion settings are correctly defined. Verify that the characteristic is properly set up in the relevant data
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