When joining Access tables on a field that has a 'Long String' type, Tableau Desktop displays an Unknown Error and the following error appears in the logs:
Database error 0x80040E21: Cannot join on Memo, OLE, or Hyperlink Object
A long string in Access is considered a MEMO field, and it is an Access limitation that joins cannot be made on such fields.
In Microsoft Access, change the field type from Long String to Short String.
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