If your local table definition does not match the server’s (it is missing the identity column), then you need to add an explicit mapping for each column (case-sensitive)
The first value is the name of the local source column, the second is destination column name.
bulk.ColumnMappings.Add("one", "one"); bulk.ColumnMappings.Add("two", "two");
This is also the case if the names don’t match up exactly.
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