This statement contains a subquery (a SELECT statement within parentheses) to represent a single value (on one side of a relational operator such as equals). Such a subquery must return exactly one row and one column; otherwise, it is unclear which value the subquery represents. This subquery has returned more than one value. This error can occur if you specify the ITEM keyword in a collection subquery with more than one element in the projection list.
Review all subqueries to make sure that they can return at most one column (by listing only one expression after SELECT) and at most one row (by testing a unique key in the WHERE clause). For a collection subquery, either drop the ITEM keyword or make sure that the projection list contains only one element.