Check the CSV file and mapping (Data Loader SDL file) for the mapped fields. If any fields attempt to update another object through the relationship field, this may be the problem.
Example:
By default, records can’t be reparented in master-detail relationships. Attempts to change the parent record will result in the above error message.
If the relationship is set up on a custom object, Administrators can allow child records to be reparented by selecting the "Allow reparenting" option in the master-detail field properties.
In order to enable "Allow reparenting" in Lightning:
000385552

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