VarChar to NVarChar causing truncate error
Well this won't happen unless


a trigger is firing on the target table, and the error happens there
the INSERT does some processing that adds enough data to make it too wide


Also, what happens with this please? This can not fail unless there is some processing.

INSERT INTO table (col1, col2)
SELECT LEFT(column1, 200)
      ,column2
  FROM tmpTable