Cursor <str> is read-only

  Explanation:  A cursor is read-only if it includes a DISTINCT
  phrase, a aggregate function, a GROUP BY, HAVING, or UNION, or
  more than one table in its FROM clause.  Read-only cursors
  cannot include FOR UPDATE clauses and cannot be used in UPDATE
  or DELETE statements.

  User Action:  Either change whatever made the cursor read-only,
  or do not attempt to update the cursor.