SQL with WITH clause too many values error

--This query is returning a "too many values" error. I'm not sure why?

   update myTable
            set var1= var2
            WHERE value1 IN (

             WITH X AS
            (
            select value1, value2, var1,var2, ROW_NUMBER()
            OVER
            (PARTITION BY value1 ORDER BY value1 desc) as rn
            from
              mytable WHERE var1 is null AND rownum>0 and rownum<=10 order by value1 asc
            )
            SELECT
            value1, value2, var2,var1
           FROM X WHERE rn=1  and var1 is null and rownum>0 and rownum<=10);