Hi Werner,
I would be interested in the export command, the import command and the complete message that is logged in the loader.log file for this error. Usually there is mentioned which row in the data file generated the error. If this is the case I would furthermore be interested in this one row (if the data file is readable and not too big to separate this one row).
Did you use the same Loader for export and import?
Best regards,
Steffen